Partially fix building on QNX 6.5.

From GitHub pull request #394; that was requested as a pull to the old
1.2 branch, not the trunk.  I also updated comments to reflect the
changes.
Fix scaling of time stamps.

Addresses GitHub issue #396.
TRAVIS: install 'libbluetooth-dev' lib
Bluetooth Linux Monitor: fix three warnings

The warnings were:
./pcap-bt-monitor-linux.c:51:1: warning: no previous prototype for 'bt_monitor_findalldevs' [-Wmissing-prototypes]
./pcap-bt-monitor-linux.c: In function 'bt_monitor_read':
./pcap-bt-monitor-linux.c:74:9: warning: unused variable 'in' [-Wunused-variable]
./pcap-bt-monitor-linux.c: At top level:
./pcap-bt-monitor-linux.c:219:1: warning: no previous prototype for 'bt_monitor_create' [-Wmissing-prototypes]
Correct return value documentation in manpages.

Manpages:
* pcap_datalink_name_to_val
* pcap_set_tstamp_type
* pcap_tstamp_type_name_to_val