Creates a new idle source.
The source will not initially be associated with any
and must be added to one with
g_source_attach() before it will be
executed. Note that the default priority for idle sources is
G_PRIORITY_DEFAULT_IDLE, as compared to other sources which
have a default priority of
The newly-created idle source.
|The caller of the function takes ownership of the data, and is responsible for freeing it.|