Core: Fix a leak on OSX that could occur in IOdarwin.mm

If a bluetooth connection isn't able to be opened with a Wiimote, then a memory leak would occur as we don't release cbt
JIT64: correctly sign-extend immediate RC values
X11Utils: Remove unneeded SendButtonEvent / SendKeyEvent utilities

This was used to send fake button or key events to every backend to
implement freelook. When I ported these to be based on wx events in
commit 5248211, I didn't realize that these were now unused, so I didn't
remove them. Do that now.
Merge pull request #752 from magcius/remove-bootleg-events

X11Utils: Remove unneeded SendButtonEvent / SendKeyEvent utilities
Fix more warnings from #579
Merge pull request #609 from Tilka/fix_warnings

Fix more warnings from #579
VideoBackendBase: Remove unused stub Initialize implementation

Both D3D and OGL have their own overrides, so this isn't used.
X11Utils: Don't depend on wx

We want to have two build targets: Main and MainNoGUI, and this code
will be linked against in both cases, so the ifdef isn't enough for
this case.

Just append to a vector of strings, and then convert it after the fact.
DolphinWX: Allow building both GUI and NoGUI at the same time

Restructure our build system so we have multiple targets. Right now we
only build MainNoGUI if we are using X11, since that's the only truly
supported backend: the OS X code actually doesn't compile, according to
comments made on IRC.
CMakeLists: Try to fix the X11 detection on OS X
Merge pull request #751 from FioraAeterna/fixsignext

JIT64: correctly sign-extend immediate RC values
Merge pull request #755 from magcius/clean-up-nogui

Allow building MainNoGUI and MainGUI simultaneously
Merge pull request #756 from magcius/remove-unused

VideoBackendBase: Remove unused stub Initialize implementation
Merge pull request #750 from lioncash/leak

Core: Fix a leak on OSX that could occur in IOdarwin.mm
DSP: DMA behaviour adjustments to fix regressions