Fix build breakage when stdint.h is included by application layer.
Include stdint and stddef in srtp.h to alleviate this requirement from the application layer.  Modified integers.h to only include the uint64_t redef when the SRTP config.h is included in the build, which should limit this to only when building libsrtp.a.  This prevents the redef from being used when the application layer includes srtp.h.
Fix build breakage at application layer when using g++.
Merge pull request #70 from saghul/pkg_config

Thanks for the contribution.
Merge branch 'master' of git://github.com/cisco/libsrtp