Use requirements scripts (freeze, minvers)

Incorporate other requirements/Makefile enhancements
Updated requirements files

Using new scripts to generate them

New version of psycopg2 released with minor fixes
Add requirements/README.rst documentation

Add pointer to that README (and note about editing) to generated files
Addresses documentation issue raised in comments on bug 3005.
Travis configuration using requirement matrix
Flask>=0.7
Sphinx>=1.1.3
no setuptools
Werkzeug<0.9 for Python 2.5
WTForms<1.0.2 (for Python 2.5)