Major update to the Makefiles

* Add support for `DISTDIR` variable
* Use `INSTALL_{PROGRAM,DATA}` rather than `cp`
* Don't add symbolic links
Automatic detection of OS to Makefile.inc
Clean up header files
Ignore somes files
Make it possible to cross compile from Linux to Windows
Create install dirs when cross compiling
Replace DISTDIR with DESTDIR
Install docs when cross compiling
Merge branch 'makefile-hackery' into Rel-2.10
small Makefile and autoconf fixes