Bug #5: Include guards became unique.

Some include guards did not fit to the expected naming convention of the
C++ language standard. This detail was fixed by the addition of a prefix.

The probability for name clashes was also reduced by the addition of a kind
of universally unique identifier as a suffix.

Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
Bug #5: Include guard generation was corrected in a build script.

A Python script constructed header files with include guards where a leading
underscore was used. This detail was fixed by the addition of a prefix.

Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
buildsystem: made search for pythoninterp, pythonlibs more resilient

fixes #26

we now search for pythonlibs, then for a pythoninterp that precisely matches the lib's version number.
Refactored the Opusfile cmake rules into own module

To properly find Opusfile on OS X (and possibly other systems too) a
hint had to be added to find the include directory of Opusfile. To keep
the CMakeLists.txt file clean, a new cmake module was created for
finding the Opusfile include directories and libraries.
Fix SDL2_image include directory hints for OS X systems
doc: added "troubleshooting" section to building.md
Include termios.h instead of the termio.h

Termio is specific for System III and System V machines and not part of
the POSIX standard (http://en.wikipedia.org/wiki/POSIX_terminal_interface#The_termios_data_structure).
buildsystem: prettified findopusfile
Merge branch 'master' of github.com:SFTtech/openage
Merge pull request #37 from svkurowski/fix_sdl2_image_hints

buildsystem: fix SDL2_image include directory hints for OS X systems
Merge pull request #39 from svkurowski/change_termio_include

util: include termios.h instead of the termio.h
Fix inclusion of pty.h header

On OS X this is part of util.h
Fixed a_star.cpp for Xcode 6.0
buildsystem: in-source builds are now blocked

error message contains instructions how to invoke cmake correctly, and how to force an in-source build.
buildsystem: added in-source-build detection to ./configure
Merge branch 'master' of github.com:SFTtech/openage
Update requirement text to include AoE II: HD for asset conversion.
Merge pull request #41 from svkurowski/fix_pty_include

Fix inclusion of pty.h header
Merge pull request #42 from jamesmintram/master

Fixed a_star.cpp for Xcode 6.0
Merge branch 'Fix_reserved_identifier_violations' of github.com:elfring/openage