grep: don't search past the end of the searched string

'*' causes the resulting RE to match 0 or more repetitions of the preceding RE:

>>> bool(re.search('.*', ''))
>>> True

This causes an infinite loop because currently we're only checking if there was
a match without looking at where we are in the searched string.

tests/test-grep.t

@@ -1,178 +1,182 b''
   $ hg init t
   $ cd t
   $ echo import > port
   $ hg add port
   $ hg commit -m 0 -u spam -d '0 0'
   $ echo export >> port
   $ hg commit -m 1 -u eggs -d '1 0'
   $ echo export > port
   $ echo vaportight >> port
   $ echo 'import/export' >> port
   $ hg commit -m 2 -u spam -d '2 0'
   $ echo 'import/export' >> port
   $ hg commit -m 3 -u eggs -d '3 0'
   $ head -n 3 port > port1
   $ mv port1 port
   $ hg commit -m 4 -u spam -d '4 0'
 
 pattern error
 
   $ hg grep '**test**'
   grep: invalid match pattern: nothing to repeat
   [1]
 
 simple
 
+  $ hg grep '.*'
+  port:4:export
+  port:4:vaportight
+  port:4:import/export
   $ hg grep port port
   port:4:export
   port:4:vaportight
   port:4:import/export
 
 simple with color
 
   $ hg --config extensions.color= grep --config color.mode=ansi \
   >     --color=always port port
   \x1b[0;35mport\x1b[0m\x1b[0;36m:\x1b[0m\x1b[0;32m4\x1b[0m\x1b[0;36m:\x1b[0mex\x1b[0;31;1mport\x1b[0m (esc)
   \x1b[0;35mport\x1b[0m\x1b[0;36m:\x1b[0m\x1b[0;32m4\x1b[0m\x1b[0;36m:\x1b[0mva\x1b[0;31;1mport\x1b[0might (esc)
   \x1b[0;35mport\x1b[0m\x1b[0;36m:\x1b[0m\x1b[0;32m4\x1b[0m\x1b[0;36m:\x1b[0mim\x1b[0;31;1mport\x1b[0m/export (esc)
 
 all
 
   $ hg grep --traceback --all -nu port port
   port:4:4:-:spam:import/export
   port:3:4:+:eggs:import/export
   port:2:1:-:spam:import
   port:2:2:-:spam:export
   port:2:1:+:spam:export
   port:2:2:+:spam:vaportight
   port:2:3:+:spam:import/export
   port:1:2:+:eggs:export
   port:0:1:+:spam:import
 
 other
 
   $ hg grep -l port port
   port:4
   $ hg grep import port
   port:4:import/export
 
   $ hg cp port port2
   $ hg commit -m 4 -u spam -d '5 0'
 
 follow
 
   $ hg grep --traceback -f 'import\n\Z' port2
   port:0:import
   
   $ echo deport >> port2
   $ hg commit -m 5 -u eggs -d '6 0'
   $ hg grep -f --all -nu port port2
   port2:6:4:+:eggs:deport
   port:4:4:-:spam:import/export
   port:3:4:+:eggs:import/export
   port:2:1:-:spam:import
   port:2:2:-:spam:export
   port:2:1:+:spam:export
   port:2:2:+:spam:vaportight
   port:2:3:+:spam:import/export
   port:1:2:+:eggs:export
   port:0:1:+:spam:import
 
   $ cd ..
   $ hg init t2
   $ cd t2
   $ hg grep foobar foo
   [1]
   $ hg grep foobar
   [1]
   $ echo blue >> color
   $ echo black >> color
   $ hg add color
   $ hg ci -m 0
   $ echo orange >> color
   $ hg ci -m 1
   $ echo black > color
   $ hg ci -m 2
   $ echo orange >> color
   $ echo blue >> color
   $ hg ci -m 3
   $ hg grep orange
   color:3:orange
   $ hg grep --all orange
   color:3:+:orange
   color:2:-:orange
   color:1:+:orange
 
 
 match in last "line" without newline
 
   $ python -c 'fp = open("noeol", "wb"); fp.write("no infinite loop"); fp.close();'
   $ hg ci -Amnoeol
   adding noeol
   $ hg grep loop
   noeol:4:no infinite loop
 
   $ cd ..
 
 Issue685: trackback in grep -r after rename
 
 Got a traceback when using grep on a single
 revision with renamed files.
 
   $ hg init issue685
   $ cd issue685
   $ echo octarine > color
   $ hg ci -Amcolor
   adding color
   $ hg rename color colour
   $ hg ci -Am rename
   $ hg grep octarine
   colour:1:octarine
   color:0:octarine
 
 Used to crash here
 
   $ hg grep -r 1 octarine
   colour:1:octarine
   $ cd ..
 
 
 Issue337: test that grep follows parent-child relationships instead
 of just using revision numbers.
 
   $ hg init issue337
   $ cd issue337
 
   $ echo white > color
   $ hg commit -A -m "0 white"
   adding color
 
   $ echo red > color
   $ hg commit -A -m "1 red"
 
   $ hg update 0
   1 files updated, 0 files merged, 0 files removed, 0 files unresolved
   $ echo black > color
   $ hg commit -A -m "2 black"
   created new head
 
   $ hg update --clean 1
   1 files updated, 0 files merged, 0 files removed, 0 files unresolved
   $ echo blue > color
   $ hg commit -A -m "3 blue"
 
   $ hg grep --all red
   color:3:-:red
   color:1:+:red
 
   $ cd ..
 
   $ hg init a
   $ cd a
   $ cp "$TESTDIR/binfile.bin" .
   $ hg add binfile.bin
   $ hg ci -m 'add binfile.bin'
   $ hg grep "MaCam" --all
   binfile.bin:0:+: Binary file matches
 
   $ cd ..