clarify getCurrentViewport

currentViewport was used as a shadowing local variable - this change is purely for code clarification.
GPU optim # 1

store uniform locations even if location returns -1. If uniform location would not be stored, many unnecessary glGetUniformLocation requests would be issued on every draw call.

This is especially pronounced if custom shaders were used which do not define the built-in shader uniforms.

Since the uniform locations cannot change once a shader is linked, a failure to look up the uniform on the first frame will also mean a failure to look it up on every following frame. By catching this early, we don't incur a driver overhead penalty per uniform per frame.
GPU optim #2

native viewport caching.

Since most apps just use one render viewport, it pays off to cache the render viewport and only issue a glGetInteger Query should the viewport have changed.

Before this, the viewport would have been queried twice a frame at least.

glGetInteger() has the potential for high driver overhead, since worst case the pipeline needs to be flushed before the query can return, and the CPU can continue issueing commands.
Merge pull request #3465 from bakercp/documentation-oftexture

Documentation oftexture
ofxiOSMapKit fixes

- Casting to correct type on assignment (ofxiOSMapKitType is a enum
clone of MKMapType anyway).
- Throws an error in Xcode 6 with llvm libc++
Merge pull request #3467 from danoli3/iOS-Fixes-Map

ofxiOSMapKit fixes
Merge pull request #3466 from bakercp/documentation-oftexture

Fixes #3455
ofLog documentation merged with ofSite
Some more ofLog documentation cleanup
ofUtils documentation, merged with ofSite and grouped
Introduction edits.
minor documentation tweaks
ofMath documentation grouping, and small fixes
Merge ofSite documentation with ofVec2f
Added OF_DEPRECATED on some old ofVec2f functions that have been marked since 006
Small fix in ofVec2f doc
Added some see also to ofVec2f
Updated ofUtils with changes made on ofSite
ofVec2f doc fixes
ofLog doc small fixes