man: add documentation for pcap_set_tstamp_precision
man: add documentation for pcap_get_tstamp_precision
build-sys: add time stamp precision man pages
linux: remove dead code
linux: fix initialization of tstamp_precision_list

We should be using tstamp_precision_list to store time stamp precisions
which we support.
Merge pull request #316 from msekletar/master

Add documentation and fix SIGSEGV when using pcap_set_tstamp_precision