Airspace/AirspaceParser: Fix wrong AS class parsing for OpenAir AS files

The existing code only checked until the first character of the
airspace class matched the valid classes which worked by lucky
coincidence.

However "RMZ" (see following patch) was always classified as "R".
Airspace: Add RMZ as known OpenAir airspace class

Implements trac enhancement request #3437.
Merge remote-tracking branch 'xcsoar/v6.7.x' into python_airspace
python: add RMZ airspace class parsing
Revert "DebugReplay: always set pressure altitude"

This reverts commit e8dec273cc4fe0bc96aba0c92dc93a91a4632828.

Seems like the IGC file spec gets overruled by the FAI Sporting Code:

FAI Sporting Code and Gliding Rules Section 3:
Gliding Edition 2013 /Appendix C / Paragraph 6.2

6.2 PR file format and testing because PRs are simpler than flight
recorders, some non-vital data fields may not be present. Pressure
altitude in the .igc file is to be recorded as zero unless it is
derived from a pressure sensor calibrated to the ICAO Standard
Atmosphere. The tests described below should be shown in the PR
files, and files from an FR should be included for comparison.
Merge branch 'python_airspace' of git://github.com/TobiasLohner/XCSoar