win32: use explicit path to "python.exe" only if it exists...
win32: use explicit path to "python.exe" only if it exists
Before this patch, "hg.bat" for Windows environment always uses
"%~dp0..\python" as explicit path to "python.exe".
This path may not be valid in some cases.
For example, on the environment using "virtualenv" python package,
both "python.exe" and "hg.bat" are placed in the same directory. In
this case, "python.exe" should be found on PATH, because virtualenv
activation script puts "python.exe" on the PATH.
This patch uses explicit path to "python.exe" only if it exists, and
expects that "python.exe" can be found on PATH otherwise.
