test/test_replaygain.sh : Prefer mawk over gawk.
test/test_replaygain.sh : Prefer mawk over gawk.

The AWK script used to generate tones for this test fails with gawk
version 4.0.1, but used to work for earlier versions. Use mawk instead
if it exists.

waitman/flac,waitman/flac,waitman/flac,waitman/flac,fredericgermain/flac,fredericgermain/flac,fredericgermain/flac,waitman/flac,fredericgermain/flac