Get rid of qwt compile error about format string.

Author: KURASHIKI Satoru <lurdan@gmail.com>

Taken from Debian patches for GC 3.0.3
Merge pull request #713 from gcoco/qwt-fix

Get rid of qwt compile error about format string.
Merge pull request #1 from GoldenCheetah/release_3.0.0

Release 3.0.0