If the guest supports client monitors config we pass it the
VDAgentMonitorsConfig message via the
QXLInterface::client_monitors_config api instead of via the vdagent.
When using config.h, it must be the very first include in all source
files since it contains #define that may change the compilation process
(eg libc structure layout changes when it's used to enable large file
support on 32 bit x86 archs). This commit adds it at the beginning
of all .c and .cpp files
