Finish DEBUGREC compile option removal

Except for the DEBUGREC_RECRUITMENT option available in C4Include.h
cmake: Use builtin support for .rc compilation on mingw

This requires CMake 2.8.4.
cmake: The netpuncher can use the Scheduler source files from libmisc
cmake: Use C++ compiler to check for X11/extensions/Xrandr.h and keysym.h

To do this, port the CHECK_INCLUDE_FILES macro from the CMake source to
C++. While at it, actually check for both headers instead of XLib.h alone.
cmake: Use C++ compiler to check for vasprintf and iconv
cmake: Link the execinfo library if necessary for execinfo.h