This commit fixes the FindXCB.cmake module for the case no components
are requested. The previous version assigned `XCB_FIND_COMPONENTS`
list to an empty variable name.
I was lucky enough to catch the bug in a corner case where both
`XCB_COMPONENTS` and `XCB_FIND_COMPONENTS` were empty and `set()`
command failed, but note this awesome CMake language supports more annoying
corner cases like `XCB_COMPONENTS` empty and `XCB_FIND_COMPONENTS`
with two elements, which results in the following `set()` invocation:
``` cmake
set(${XCB_FIND_COMPONENTS[0]} ${XCB_FIND_COMPONENTS[1]})
```
So always beware of CMake secret charms...
* Added FindXCB.cmake script
* Added AutoPointer wrapper for automatically free'ing pointers
* Huge commit: Ported linux implementation of sfml-window to xcb
* Xcb is now used for window creation, event loop etc
* As GLX is linked to Xlib, that part of the implementation
still uses Xlib.
* Also, some keyboard related (such as XLookupString) stuff
is still Xlib, as xcb does not have it (yet?).
* Replaced some enums with the xcb equivalents
