Re-sort pinned requirements with LC_ALL=C

This allows seeing changes in diffs
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.