Compilation with traces now enabled by default

[Aleksander Morgado]

Hey,

Printed human-readable traces of the messages have proven to be quite
useful when debugging issues with libqmi, so I updated the build to
*always* compile the printable traces support (the old --with-traces or
-DMESSAGE_ENABLE_TRACE).

Applications can decide whether they want to include the traces as
g_debug()s by using the new `qmi_utils_set_traces_enabled(gboolean)' [1]
method. qmicli does it when using --verbose, and ModemManager does it
when log level is DEBUG.

Cheers!

[1]
http://www.lanedo.com/~aleksander/libqmi/html/libqmi-glib-Common-utilities.html#qmi-utils-set-traces-enabled

-- 
Aleksander