We currently hardcode this device when spicec needs to record with
alsa. However, this doesn't interact well with PulseAudio, which
means that if something is already using the recording device, spicec
won't be able to open it again.
Using "default" as the device will let spicec use the PulseAudio
alsa support and will avoid this issue.
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
