heredoctest: use the same dict for local/global contexts as in doctest

In order to mimic module-level evaluation, globals and locals should be the
same object, so doctest does not pass separate locals dict.

https://docs.python.org/2.7/reference/simple_stmts.html#exec

This fixes NameError in the following example:

    >>> import foo
    >>> def bar():
    ...     foo  # must exist in globalvars

tests/heredoctest.py

@@ -1,19 +1,18 b''
 import sys
 
 globalvars = {}
-localvars = {}
 lines = sys.stdin.readlines()
 while lines:
     l = lines.pop(0)
     if l.startswith('SALT'):
         print l[:-1]
     elif l.startswith('>>> '):
         snippet = l[4:]
         while lines and lines[0].startswith('... '):
             l = lines.pop(0)
             snippet += "\n" + l[4:]
         c = compile(snippet, '<heredoc>', 'single')
         try:
-            exec c in globalvars, localvars
+            exec c in globalvars
         except Exception, inst:
             print repr(inst)

tests/test-unified-test.t

@@ -1,124 +1,129 b''
 Test that the syntax of "unified tests" is properly processed
 ==============================================================
 
 Simple commands:
 
   $ echo foo
   foo
   $ printf 'oh no'
   oh no (no-eol)
   $ printf 'bar\nbaz\n' | cat
   bar
   baz
 
 Multi-line command:
 
   $ foo() {
   >     echo bar
   > }
   $ foo
   bar
 
 Return codes before inline python:
 
   $ sh -c 'exit 1'
   [1]
 
 Doctest commands:
 
   >>> print 'foo'
   foo
   $ echo interleaved
   interleaved
   >>> for c in 'xyz':
   ...     print c
   x
   y
   z
   >>> print
   
+  >>> foo = 'global name'
+  >>> def func():
+  ...     print foo, 'should be visible in func()'
+  >>> func()
+  global name should be visible in func()
 
 Regular expressions:
 
   $ echo foobarbaz
   foobar.* (re)
   $ echo barbazquux
   .*quux.* (re)
 
 Globs:
 
   $ printf '* \\foobarbaz {10}\n'
   \* \\fo?bar* {10} (glob)
 
 Literal match ending in " (re)":
 
   $ echo 'foo (re)'
   foo (re)
 
 Windows: \r\n is handled like \n and can be escaped:
 
 #if windows
   $ printf 'crlf\r\ncr\r\tcrlf\r\ncrlf\r\n'
   crlf
   cr\r (no-eol) (esc)
   \tcrlf (esc)
   crlf\r (esc)
 #endif
 
 Combining esc with other markups - and handling lines ending with \r instead of \n:
 
   $ printf 'foo/bar\r'
   fo?/bar\r (no-eol) (glob) (esc)
 #if windows
   $ printf 'foo\\bar\r'
   foo/bar\r (no-eol) (glob) (esc)
 #endif
   $ printf 'foo/bar\rfoo/bar\r'
   foo.bar\r \(no-eol\) (re) (esc)
   foo.bar\r \(no-eol\) (re)
 
 testing hghave
 
   $ "$TESTDIR/hghave" true
   $ "$TESTDIR/hghave" false
   skipped: missing feature: nail clipper
   [1]
   $ "$TESTDIR/hghave" no-true
   skipped: system supports yak shaving
   [1]
   $ "$TESTDIR/hghave" no-false
 
 Conditional sections based on hghave:
 
 #if true
   $ echo tested
   tested
 #else
   $ echo skipped
 #endif
 
 #if false
   $ echo skipped
 #else
   $ echo tested
   tested
 #endif
 
 #if no-false
   $ echo tested
   tested
 #else
   $ echo skipped
 #endif
 
 #if no-true
   $ echo skipped
 #else
   $ echo tested
   tested
 #endif
 
 Exit code:
 
   $ (exit 1)
   [1]