Use g_try_malloc/g_free/g_strdup consistently.

Use g_try_malloc/g_free/g_strdup consistently.

Avoid plain malloc()/free() in sr/srd, especially in the API calls.
Also avoid g_malloc*() in favor of g_try_malloc*().

Use g_strdup() instead of strdup() so that we can use g_free()
consistently everywhere.

Exceptions: Stuff that is allocated via other libs (not using glib),
should also be properly free'd using the respective free-ing function
(instead of g_free()). Examples: Stuff allocated by libusb, libftdi, etc.

Also, use sr_err() instead of sr_warn() for actual errors. sr_warn() is
meant for non-fatal/uncritical warnings.