Added assert if SDL background thread locks up, also tidied trace logs.
Added a --disable-test-XXXX to configure stript to disable the compile/link test of a modules usability. This is needed as later Ubuntu systems do not seem to be able to compile some libraries where the -lXXX on the command line precedes the conftest.c file. As I cannot figure out how to change standard macros like AC_LINK_IFELSE(), nor believe we are expected to, the only thing I can think of is to disable the test. The test is actually there to prevent accidental detection of the native pkg-config module during cross compile.