exewrapper: adapt for legacy HackableMercurial We give up using CPython's PythonXX.lib import libraries (and Python.h), and now "manually" call the LoadLibrary() / GetProcAddress() Windows API's instead. If there is a "hg-python" subdirectory (the canonical directory name for HackableMercurial's private Python copy) next to the hg.exe, we load the pythonXX.dll from there (feeding an absolute path to LoadLibrary) and we set Py_SetPythonHome() to that directory, so that the Python libraries are used from there as well. If there is no "hg-python" subdir found next to the hg.exe, we do not feed an absolute path to LoadLibrary. This continues to allow to find a globally installed Python DLL, as before this change - that is, without having to edit, delete, rename, or configure anything. Note that the hg.exe built is still bound to a *specific* major version of the pythonXX.dll (e.g. python27.dll). What version it is, is inferred from the version of the python interpreter that was used when calling setup.py. For example C:\python27_x86\python.exe setup.py build_hgexe -i --compiler=mingw32 builds a hg.exe (using the mingw32 tool chain) bound to (x86) Python 2.7. And C:\python27_x86\python.exe setup.py build_hgexe -i builds the same using the Microsoft C compiler/linker. (Note that the Microsoft toolchain combined with x64 CPython can be used to build an x64 hg.exe.) setup.py is changed to write the name of the pythonlib into the generated header file "mercurial/hgpythonlib.h", which is #included by exewrapper.c. For a Python 2.7 build, it for example contains: #define HGPYTHONLIB "python27" exewrapper.c then uses HGPYTHONLIB for the name of the Python dll to load. We don't want to track mercurial/hgpythonlib.h, so we add it to .hgignore.