Fixed a variable name warning

The name 'size' is already used as an instance attribute, so it should
not be used as a local variable name. XCode warned about this.

Change-Id: Ifeb493a27b5984d914a20390028ca307ee91cf91
Reviewed-on: https://iffwww.iff.kfa-juelich.de/review/122
Reviewed-by: Josef Heinen <j.heinen@fz-juelich.de>
Use Core Text for text rendering in GKSTerm

Text rendering using Core Graphics is deprecated since OS X 10.9.
This commit uses Core Text instead, as recommended by Apple.

Change-Id: Ib286d43d78848b48b5c8f4b0db06f43d97aaf5ea
Reviewed-on: https://iffwww.iff.kfa-juelich.de/review/123
Reviewed-by: Josef Heinen <j.heinen@fz-juelich.de>