Have configure check for header and library when bzip is enabled.
AC_CHECK_LIB requires a second argument, a function to test for.
Simplify the autoconf that checks for bzip2 headers/libraries.

Pull the header/library checks outside of the existing AC_MSG_XX
conditionals, otherwise the autoconf output gets messy.

Add matching checks for the snappy headers/libraries.
whitespace cleanup
Merge pull request #522 from wiredtiger/bzip_configure

Have configure check for header and library when bzip and/or snappy are enabled.