strings/memory: constify and func_attr.

Fix MB_COPY_cHAR() to accept const pointers.
strings: Enable -Wconvert.
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.
Wconversion: fix #1578
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.
mch_write -> term_write

Switch from POSIX's write() to fwrite(stdout,...) and disable buffering
since vim buffers output explicitly and flushes when needed, like when a
key is typed.
mch_init -> term_init
update mch_suspend

Use the portable uv_kill.
Don't bother with archaic BeOS.
mch_early_init() -> early_init().

Move general initialization functions to early_init, which simplifies
test/unit/helpers.lua, which requires all these functions.
Merge pull request #1186 from splinterofchaos/write

Non-unix-specific os_unix function.
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
Travis: Prepare for OS X builds.

 * Use bot-ci script at to set up prebuilt dependencies.
 * Make CI scripts more consistent.
Merge pull request #1538 from fwalch/multi-os

Travis: Prepare for  OS X builds.
Merge pull request #1497 from splinterofchaos/const-attr

constify and func-attribute memory.c and strings.c
Fix SegFault when getting full path for files
Merge pull request #1582 from LBEaston/FixSegFault

Fix SegFault when entering Command(q:) or Search(q/) History
deps: Add libtickit/libtermkey as dependency

The new terminal UI will be implemented on top of those libraries