start implementing hsla image-filter
touchups to hsla work
scons: fix behavior of scons --clean install
Merge branch 'master' of github.com:mapnik/mapnik into hsla-filter
+ image-filters: add support for an optional function like syntax
+ image-filters

accept following syntax in agg-stack-blur:

```c++
agg-stack-blur
agg-stack-blur()  // rx = 1, ry = 1

agg-stack-blur(10) // rx = 10, ry = 1

agg-stack-blur(10,10) // rx=10,ry = 10

```
fix serialization of agg-stack-blur and hsla filters
+ untabify
+ update clipper to r304
Merge pull request #1742 from mapnik/hsla-filter

Hsla filter
+ image-filters: add colorize-alpha filter
+ image-filters: parse hsla string directly
benchmark: link CoreFoundation on os x to enable instruments profiling
benchmark: avoid copying test struct and add test of clipper
Merge branch 'master' of github.com:mapnik/mapnik
add missing test file
finish hsla transformation image-filter
+ treat .h as c++
fix logic error causing direct-image-filters to not be enabled unless normal image-filters are also enabled
+ add deps/agg directory