[PATCH] allow 'const' strings to be passed to msGetCharacterSize() + fix a warning

[pere@…]

The function msGetCharacterSize() should be able to accept const
strings as the font specifier.  Especially since it at the moment is
passing it to gdImageStringFT(), which only read the string and don't
write to it.  At the moment, the 'constness' is removed in at least
one place.  This patch move this 'constness' removal from
msGetMarkerSize() to msGetCharacterSize() in preparation for libgd to
fix the prototype of gdImageStringFT().

The code should also use floating point values as the ptsize and angle
argument when calling gdImageStringFT(), to make sure the variables
matchines the type of the recieving function.

This patch fixes these two issues.

This patch reduces the number warnings when compiling the source with
lots of warning flags enabled.

[pere@…]

patch for msGetCharacterSize()

[hobu]

Adding Steve to see if we can easily squish this one...