util: avoid using hashlib on Python < 2.5 (issue2278)
The following patch allows the use of python2.4 with a standalone
hashlib rather than assuming that python2.5 is in use when hashlib is
imported successfully.
% file replaced with directory
adding a
% should fail - would corrupt dirstate
abort: file 'a' in dirstate clashes with 'a/a'
% directory replaced with file
adding a/a
% should fail - would corrupt dirstate
abort: directory 'a' already in dirstate
% directory replaced with file
adding b/c/d
% should fail - would corrupt dirstate
abort: directory 'b' already in dirstate