Revert "roundgpx: Behave just like gpst, truncate decimals instead of rounding"

This reverts commit f5b60e233422c491319fa0c031c445b8a304018e. Can't use
truncate because floating point sucks. Things like lon=4.8996 is changed
to 4.899599. Fuck that shit.

b1e7921e-f545-11e2-ac1d-001f3b596ec9