build: improve X11 detection on OS X

/usr/X11R6 doesn't exist on OS X per default (anymore). Therefore add
PATHS to all X11 detection modules pointing to the Xquarz installation
directory in /opt/X11.
For FindX11 it was also necessary to ensure that the frameworks are
searched as last (after PATHS) otherwise it could happen that X11 headers
of a framework (e.g. Tk.framework) were used.
rdtk: build samples only if WITH_SAMPLE is enabled
Mac: set policy to silent cmake >= 3.0 warnings

Set the following policies to "OLD" if cmake version is greater than
2.8.12:

CMP0026 - Disallow use of the LOCATION target property
CMP0045 - Error on non-existent target in get_target_property
build: cmake 3.1 compatibility

* fix problem with REMOVE_DUPLICATES on undefined lists
* since 3.1 file(GLOB FILEPATHS RELATIVE .. returns single / instead of // as
  previously - necessary adoptions for regex and matches done. Should
	work with all cmake versions.

Tested with 3.1.0-rc3
rdtk/shadow: install libraries versioned
Merge pull request #2276 from bmiklautz/build_fixes

Build fixes
xfreerdp: fix RDP order color conversion

Note: /gdi:sw was working fine, this commit fixes /gdi:hw

* calculate color channel shifts based on X11 visual color masks
* fast path to skip conversion if visual color masks equal rdp color masks
* successfully tested 8/15/16/24/32 bpp rdp sessions on 16/24/32 bpp visuals
Merge pull request #2277 from nfedera/fix-2014-12-15-01

xfreerdp: fix RDP order color conversion
Update drdynvc_main.c

fixed memory leak
Merge pull request #2278 from erobertor/master

Update drdynvc_main.c
core: fix problem with data for unknown channel

Some buggy server(s) send data for channels that weren't announced or
negotiated. When processing this data FreeRDP had a problem and always
used the last channel in the channels list even if it wasn't responsible
for the data. Depending on how the channel handled the data this could
lead to different kind of problems and also segmentation faults.

Now data for unknown channels is ignored and not processed further.
Merge pull request #2279 from bmiklautz/channel_fail

core: fix problem with data for unknown channel
libfreerdp-core: server synchronized access to dvc channel seq.
Merge pull request #2283 from llyzs/llyzs

libfreerdp-core: server synchronized access to dvc channel seq.