Add new build options for choosing client backend and disabling nested input driver.

Signed-off-by: Laércio de Sousa <laerciosousa@sme-mogidascruzes.sp.gov.br>
Surround nested-input related code with "#ifdef NESTED_INPUT".

Signed-off-by: Laércio de Sousa <laerciosousa@sme-mogidascruzes.sp.gov.br>
Add new XCB backend, based on Xephyr code.

Signed-off-by: Laércio de Sousa <laerciosousa@sme-mogidascruzes.sp.gov.br>
Add support for xorg.conf options "Xauthority" and "Fullscreen".

Signed-off-by: Laércio de Sousa <laerciosousa@sme-mogidascruzes.sp.gov.br>
Add support for xorg.conf "Output" option.

Signed-off-by: Laércio de Sousa <laerciosousa@sme-mogidascruzes.sp.gov.br>