Simplify Dpkg::Source::Compressor by using the extended fork_and_exec()

Simplify Dpkg::Source::Compressor by using the extended fork_and_exec()

* scripts/Dpkg/Source/Compressor.pm: Replace the multiple compress_*
functions by a single compress() function that accepts the same
parameters than fork_and_exec(). The exec parameter is replaced
with the right compressor/decompressor invocation, and some other
parameters have default values.
Same for uncompress_* replaced by uncompress().
* scripts/dpkg-source.pl: Update accordingly to use the new syntax.