Log Message:
libgeotiff: Update to 1.6.0

Upstream NEWS:

  Add support for OGC GeoTIFF 1.1

  Expose GTIFGetPCSInfoEx(), GTIFGetProjTRFInfoEx(),
  GTIFGetGCSInfoEx(), GTIFGetDatumInfoEx(), GTIFGetEllipsoidInfoEx(),
  GTIFGetPMInfoEx(), GTIFGetUOMLengthInfoEx() and
  GTIFGetUOMAngleInfoEx() so that users can specify their own PROJ
  context

  Add GTIFKeyGetASCII(), GTIFKeyGetSHORT() and GTIFKeyGetDOUBLE() as
  safer variants of GTIFKeyGet() with type checking

  autotools build: enable build in a separate tree from source (#37)
  (fixes #28)

  Use pkg-config for libtiff detection