Remove NeXTSTEP references

Remove trailing whitespace as well.
Remove Atari MiNT references
Remove OS/2 references

Paul Slootman was removed from the top of os_unix.c as OS/2 is no longer
supported, but is still credited in runtime/doc/intro.txt.
Fix newline substitution.

Problem  : Command `s/\n//` is being translated into a call to do_join
           with a count of 1. But do_join asserts its precondition count
           >= 2, which is causing the program to abort.
Note     : This in fact revealed bigger problems: generated join command
           line count, as well as reported substitutions/lines were
           wrong in several cases, since patch 7.4.232.
           See:
           [patch] http://markmail.org/message/vo7ruair5raccawp
           [issue] https://code.google.com/p/vim/issues/detail?id=287
Solution : - Don't generate join command for single-line-range case.
           - Make generated join command include:
             * lines in range + 1, when range doesn't end at last line.
             * lines in range, when range ends at last line.
           - Make reported substitutions/lines always be
             number-of-lines-joined - 1.
Merge pull request #1533 from elmart/fix-sub-newline-abort

Fix newline substitution causing abort
Merge pull request #1491 from Pyrohh/os2-and-misc-cleanup

Remove MiNT, NeXTSTEP, OS/2 References
Merge pull request #1538 from fwalch/multi-os

Travis: Prepare for  OS X builds.
Travis: Perform installation test on 32-bit build.
Travis: Add flag to force building of dependencies.