docs: Remove BeOS/Haiku remnants
docs: Remove VAX remnants
docs: Remove EBCDIC remnants
docs: Remove 'osfiletype' remnants

Even when this was finally removed 6 months ago in b2b920f, it had
already been disabled for a while. Due to this, just remove all remnants
of the option as opposed to putting a placeholder like what was done for
'shortname'and 'cryptmethod'.
docs: Remove RISC OS remnants
docs: Remove OS/390 remnants
docs: Remove Photon remnants

Also get rid of some platform references made irrelevant by the removal
of their respective platform specific GUI code.
docs: Fix incorrect Mac path references
Merge pull request #1628 from Pyrohh/misc-cleanup

More misc. platform cleanup
Install gettext.
Set DYLD_LIBRARY_PATH.
Use default Clang on OS X.
Don't ignore OS X failures.
Add new 'unittest' target.
Try different compilers.
Disable Linux builds.
Try different GCC version.