Merge pull request #44 from demorest/master

parfile.py: Add PMLAMBDA, PMBETA, PX to list of keywords. -- Thanks, Paul!
Make sure we convert P0 and P1 to F0 and F1 even if no errors
Make sure we convert P0 and P1 to F0 and F1 even if no errors, for real this time
Ensure that clipping is off if we are using zero-DMing
Fix problem with undisplayed data in plots of folded makedata timeseries
Greatly improved robustness of inf file reading and parsing
Fixed error checking on chk_str2double which could be erroneously tripped
Added some code so we can process archived PSRFITs search-mode data with no OFFS_SUB set