Upgrade MITAB driver to version 1.6.1

[Daniel Morissette]

The version of the MITAB library in GDAL trunk is v1.5.1. We need to upgrade to MITAB 1.6.1 which contains the following changes/fixes:

Version 1.6.1 (2007-03-30)
--------------------------

- Added "Quick Spatial Index Mode" which generates a non-optimal spatial
  index (similar to MITAB 1.5 and older) but results in faster write
  time than the optimized index generated by v1.6.0+ (bug 1669)
  (Thanks to Safe Software for funding this.)

- Added mitab_c_set_quick_spatial_index_mode() to C API (bug 1669)

- Fixed problem writing collections where MITAB was sometimes trying to 
  read past EOF in write mode (bug 1657).

- Fixed another problem writing collections when the header of objects 
  part of a collection were split on multiple blocks (bug 1663)

- Added missing NULL pointer checks in SetPenFromStyleString(), 
  SetBrushFromStyleString() and SetSymbolFromStyleString() (bug 1670)


Version 1.6.0 (2007-02-15)
--------------------------

- Improved generation of the .map's internal spatial index and object
  data blocks to produce an optimal r-tree, resulting in performance 
  improvements of up to 30 times faster on some spatial searches, 
  matching the perfomance of files generated by MapInfo. (bug 1585)
  (Thanks to Aircom International (Andrew Blake) for funding this.)

- Fixed problem with null brush bg color becoming black when parsing
  style strings (bug 1603)

- Added mitab_is_field_indexed() and mitab_is_field_unique() to C API
  (bug 1621)

[Daniel Morissette]

Done.

gdal/ogr/ogrsf_frmts/mitab/*.* upgraded to MITAB 1.6.1 in SVN r11171

gdal/ogr/ogrsf_frmts/mitab/drv_mitab.h updated (SVN r11170) to mention new SPATIAL_INDEX_MODE=QUICK layer creation option