Fix for BUG #492:  UHD: set_time_unknown_pps() fails with GPSDO installed
- Added polling for PPS time change after setting time from GPSDO.
X300: Added UHD support for TX FE
Merge 'maint' into x300/bug513
tx fe corrections: fixing mixed tabs / spaces, other horrible whitespace cruft
Merge branch 'maint' into uhd/bug492

Conflicts:
	host/lib/usrp/b200/b200_impl.cpp
usrp_burn_mb_eeprom: write all changes to the EEPROM at once

* Utility was unnecessarily wearing out EEPROMs by calling separate writes for each key
Updated documentation

* Updated UHD documentation-related URL's after manual overhaul
* Updated NI-USRP URL to link to NI-USRP 1.3