dispatch: give better error message when cwd doesn't exist (issue2293)

Previous behavior wasn't very helpful:
$ hg st foo
abort: No such file or directory

Now we tell more about what failed:
abort: error getting current working directory: No such file or directory

mercurial/dispatch.py

@@ -366,7 +366,12 b' def _dispatch(ui, args):'
         os.chdir(cwd[-1])
 
     # read the local repository .hgrc into a local ui object
-    path = cmdutil.findrepo(os.getcwd()) or ""
+    try:
+        wd = os.getcwd()
+    except OSError, e:
+        raise util.Abort(_("error getting current working directory: %s") % 
+                         e.strerror)
+    path = cmdutil.findrepo(wd) or ""
     if not path:
         lui = ui
     else:

tests/test-dispatch

@@ -3,6 +3,8 b''
 
 "$TESTDIR/hghave" no-outer-repo || exit 80
 
+dir=`pwd`
+
 hg init a
 cd a
 echo a > a
@@ -19,8 +21,12 b' cat = -r null'
 EOF
 hg cat a
 
+echo '% working directory removed'
+rm -rf $dir/a
+hg --version
+
 echo '% no repo'
-cd ..
+cd $dir
 hg cat
 
 exit 0

tests/test-dispatch.out

@@ -33,5 +33,7 b' use "hg -v help cat" to show global opti'
 % [defaults]
 a
 a: No such file in rev 000000000000
+% working directory removed
+abort: error getting current working directory: No such file or directory
 % no repo
 abort: There is no Mercurial repository here (.hg not found)!