Allow user defined bounds

[vpicavet]

The bounds cannot be set by the user, and sometimes the bounds written by mitab are not the ones we want.

With this patch, when exporting a tab file, mitab looks for a bound corresponding to the projection, defined in two tables :

• the default table, hard coded in mitab source code (mitab_bounds.cpp)
• a table defined by the user in a text file

Patch :
https://gist.github.com/vpicavet/5569987

This bug is related to #2 and patches should be applicated in this order :

$ patch -p1 < mitab-L93-EPSG2154.patch
$ patch -p1 < mitab-precision.patch
$ patch -p1 < mitab-userProvidedBounds.patch

The patch has been tested against the mitab version in GDAL svn 25454