improve header parsing
added code for samtools/libbam free bam input and name collation
added bgzf writing code
add bam header writing code, fix  bgzf code in writing headers
added/fixed code for libbam free bam file writing
fixed code for adding auxiliary tags in libbam free bam writing
split testbamwriter into two sections (with/without libbam)
removed dependence from sam.h/bam.h if package is configure using the --enable-bamonly option
update autoconf/automake scripts to not require a samtools installation if --enable-bamonly is given for configure