exewrapper: add comments about PYTHONHOME This has been a repeating source of confusion for users of HackableMercurial. Note that users of HackableMercurial should *not* and are *not* expected to set PYTHONHOME.

exewrapper: report name of failed private DLL in error message Same as in preceding change, but this time it's for the private Python of HackableMercurial (in hg-python directory next to the hg.exe).

exewrapper: report name of failed DLL in error message This uses C string literal concatenation. Example output: $ hg version abort: failed to load Python DLL python27.dll Note that HGPYTHONLIB does not contain the trailing .dll, which works here because the documentation of LoadLibrary [1] says, that if no file name extension is specified in the filename parameter, the default library extension .dll is appended. See [2] for a motivation of this change. [1] https://msdn.microsoft.com/en-us/library/windows/desktop/ms684175(v=vs.85).aspx [2] https://selenic.com/pipermail/mercurial/2015-August/048627.html