OpenGL/Dynamic: Define HAVE_DYNAMIC_MAPBUFFER for Win32 (for ANGLE)

Fix ANGLE build - load glMapBufferOES dynamically
Win32 workaround: undef OPAQUE and TRANSPARENT macros

Some Win32 headers define OPAQUE and TRANSPARENT as preprocessor
defines. Undefine them to avoid name conflict.
TCHAR compatibility fixes

Fixes for Win32 UNICODE build
Introduce new variable USE_WIN32_RESOURCES

New build variable and preprocessor macro USE_WIN32_RESOURCES to
determine if the Win32 resources mechanism or the Unix mechanism should
be used. USE_WIN32_RESOURCES is set to true for Win32 builds, unless SDL
is used.
Makefile: Introduce new variable ZLIB_PREFIX

Allow explicitly specifying a zlib installation prefix using the
ZLIB_PREFIX variable
Manual patches - minor changes - Fixes for #3375 and #3376
Merge branch 'master' of git://git.xcsoar.org/xcsoar/master/xcsoar

Conflicts:
	doc/manual/en/ch03_navigation.tex
	doc/manual/en/ch05_glide_computer.tex