Compile for Windows

[jonblack]

Make it possible to compile for Windows. An option is to use the MingW compiler.

[SchiggaDigga]

Needed some patches for MingW:

• various: removed 'P_WIN'; replaced 'P_WIN' and '_MSC_VER' with '_WIN32' where appropriate
• mkdssp.cpp/mkhssp.cpp: fixed '_getch()' for Windows; unused 'char ch' not needed
• progress.cpp: changed 'uint' to 'unsigned int'
• autogen.sh: added '-I m4' to 'aclocal'
• mkhssp.cpp: fixed 'outfilename.c_str()' for Windows (wchar_t); added 'string()' to 'outfilename'

xssp-3.0.2-mingw.patch