Remove MEGAGLEST_VERSION for MG_VERSION_H_CONTENTS

I noticed that mk/macos/CMakeLists.txt has special code for extracting the
megaglest version , but its already done in CMakeLists.txt. This removes the
duplicate detection and changes the users of MEGAGLEST_VERSION to
MG_VERSION_H_CONTENTS.
Change library search path on MacOS

When using mac ports GL/gl.h ends up outside the cmake search paths for
libraries and includes. By adding them to mk/macos/CMakeLists.txt they are now
available and make it possible to build g3d_viewer along with the rest of
megaglest. To make this work properly I had to move the inclusion of
mk/macos/CMakeLists.txt further up the master CMakeLists.txt so merged both IF
APPLE tests in to one.

This has built successfully through xcode and gnumake.
Remove unneeded comments

These comments indicated TODO items and are no longer needed in the final change.
Revert change to quoting

Accidentally included a change of quoting which isn't related to the diff at
hand; reverted with this commit.
Remove duplicate DCUSTOM_DATA_INSTALL_PATH

Within 5 lines CUSTOM_DATA_INSTALL_PATH is defined twice resulting in lots of
compiler warnings; eg

[ 11%] Building CXX object source/shared_lib/sources/streflop/CMakeFiles/streflop.dir/libm/flt-32/s_atanf.cpp.o
In file included from <built-in>:175:
<command line>:7:9: warning: 'CUSTOM_DATA_INSTALL_PATH' macro redefined
        ^
<command line>:2:9: note: previous definition is here
        ^

This removes the second definition.

Conflicts:
	CMakeLists.txt
Merge pull request #39 from goetzk/change-library-search-paths-on-osx

Change library search paths on osx
Merge pull request #40 from goetzk/remove-mac-specific-version-detection-code

Remove mac specific version detection code
Merge pull request #41 from goetzk/remove-duplicate-custom-data-install-path-definition

Remove duplicate DCUSTOM_DATA_INSTALL_PATH
- update miniz code to 1.15
different rendering of resources in teammode
render messagebox in a way that allows more text.

And default message box height is raised a bit to avoid trouble with 
long messages in scenarios.
default GraphicMessageBox size adjusted