GPS reporting impossible readings

[imondrag]

This was first noticed in PR #39 when the GPS altitude was being reported as -18 and 11574.799805 on different test builds. spkm and spkn were also reporting values greater than, or near, 1000 which means the GPS module must have been moving at that speed in km/hr.

gps_hdop,node_id=ARB000,source=node,commit_hash=b3c9946493e2258e82bc90b57f67c071d7d33db6 value=1.100000
gps_altitude,node_id=ARB000,source=node,commit_hash=b3c9946493e2258e82bc90b57f67c071d7d33db6 value=11574.799805
gps_fix,node_id=ARB000,source=node,commit_hash=b3c9946493e2258e82bc90b57f67c071d7d33db6 value=3.000000
gps_cog,node_id=ARB000,source=node,commit_hash=b3c9946493e2258e82bc90b57f67c071d7d33db6 value=79.800003
gps_spkm,node_id=ARB000,source=node,commit_hash=b3c9946493e2258e82bc90b57f67c071d7d33db6 value=1812.800049
gps_spkn,node_id=ARB000,source=node,commit_hash=b3c9946493e2258e82bc90b57f67c071d7d33db6 value=978.799988

One probable cause may be the power configuration. Right now the testing node is powered by the programmer as opposed to battery power. It has two ultrasonic sensors, a decagon, a DO sensor and (just recently) an autosampler attached.