Soft dependency on PIL or Pillow

Please do not force a dependency on PIL. Many prefer to use Pillow.
gentler field validation, allow DateTime type

allow OGRDateTime fields; only validate fields in the whitelist
Merge pull request #114 from probabble/patch-1

gentler field validation, allow DateTime type
Bumped to 1.46.8 with addition of ogr.OFTDateTime in Vector provider
Bumped to 1.46.9 with addition of ogr.OFTDate and ogr.OFTTime in Vector provider
Prefixed some Postgres functions in VecTile with "ST_"
Prefixed more Postgres functions in VecTile with "ST_"
Bumped to 1.46.10 with "ST_" prefixes for most Postgis functions in VecTile provider
Use coordinate generators as generators

This prevents tilestache-seed.py from inadvertently pre-calculating
coordinates, which wastes time and memory when used with large bounding boxes
at high zooms.
initial redis cache provider for TileStache
Use xrange in the generator function

xrange is in turn a generator, so we can further reduce memory use.
Merge pull request #115 from mojodna/generator-usage

Use coordinate generators as generators
split host,port,db and implement locks
use setnx
Merge pull request #109 from fabianbuechler/patch-1

Soft dependency on PIL or Pillow
Merge pull request #116 from perrygeo/redis

Redis cache provider
Logged recent changes and added Redis to Makefile
api docs
might help if we actually passed the kwargs
Applied Nelson's doc patch