check-code: forbid "\S" in egrep regular expression

BSD `egrep` does not like it. So let's forbid it.

Differential Revision: https://phab.mercurial-scm.org/D610

contrib/check-code.py

@@ -119,6 +119,7 b' testpats = ['
     (r'\[[^\]]+==', '[ foo == bar ] is a bashism, use [ foo = bar ] instead'),
     (r'(^|\|\s*)grep (-\w\s+)*[^|]*[(|]\w',
      "use egrep for extended grep syntax"),
+    (r'(^|\|\s*)e?grep .*\\S', "don't use \\S in regular expression"),
     (r'(?<!!)/bin/', "don't use explicit paths for tools"),
     (r'#!.*/bash', "don't use bash in shebang, use sh"),
     (r'[^\n]\Z', "no trailing newline"),

tests/test-context-metadata.t

@@ -36,7 +36,7 b' Tests about metadataonlyctx'
   date:        Thu Jan 01 00:00:00 1970 +0000
   summary:     Changed
   
-  $ hg --config extensions.metaedit=$TESTTMP/metaedit.py metaedit 'parents=0' 2>&1 | egrep '^\S*Error'
+  $ hg --config extensions.metaedit=$TESTTMP/metaedit.py metaedit 'parents=0' 2>&1 | egrep '^RuntimeError'
   RuntimeError: can't reuse the manifest: its p1 doesn't match the new ctx p1
 
   $ hg --config extensions.metaedit=$TESTTMP/metaedit.py metaedit 'user=foo <[e-mail]>'