Added Freetype support routines for the GD driver.
Added Freetype support routines for the GD driver.

Freetype support has been added to the GD family of drivers using the
plfreetype.c module, and implemented as a driver-specific optional extra
invoked via the -drvopt command line toggle. It uses the "PLESC_HAS_TEXT"
command for rendering within the driver.

Freetype support is turned on/off at compile time by defining "HAVE_FREETYPE".

To give the user some level of control over the fonts that are used,
environmental variables can be set to over-ride the definitions used by
the five default plplot fonts.

Freetype rendering is used with the command line "-drvopt text".
Anti-aliased fonts can be used by issuing "-drvopt text,smooth"

svn path=/trunk/; revision=3888

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