Revision 1888018

Merge r1888017 from trunk:

Follow up to r1887279: fix new APR_TRY_COMPILE_NO_WARNING.

AC_LANG_PROGRAM generates an "int main()" prototype which some compilers warn
about. Restore AC_LANG_SOURCE to manually set the correct main() but do not
#include "confdefs.h" if it is inlined already by AC_LANG_SOURCE (i.e.
check whether PACKAGE_NAME is already defined).

Github: closes #25