revsets: more informative syntax error message I came across a case where an internal command was using a revset that I didn't immediately pass in and it was difficult to debug what was going wrong with the revset. This prints out the revset and informs the user that the error is with a rebset so it should be more obvious what and where the error is.

--- a/tests/test-revset.t	Mon Apr 13 21:06:21 2015 -0700
+++ b/tests/test-revset.t	Mon Apr 13 20:53:05 2015 -0700
@@ -1535,7 +1535,7 @@
 
 test error message of bad revset
   $ hg log -r 'foo\\'
-  hg: parse error at 3: syntax error
+  hg: parse error at 3: syntax error in revset 'foo\\'
   [255]
 
   $ cd ..