Fix postgresql connection leaks

Return connection to pool on connection error (see #1708)
Fix leaks on persist_connection=false (#1711)

Includes testcase for #1711
- scons help cosmetics
- avoid using double quotes when already escaping as string
- avoid using clog/cerr in sqlite plugin (use mapnik::logging facilities instead)
+ mapnik::projection add operator<<
+ fix assignment operator #1776
Fix checks in Map::resize().
Merge pull request #1764 from strk/master_connection_leaks

Fix postgresql connection leaks
Simplify halo rendering by reducing number of loop indices.
Merge branch 'master' of github.com:mapnik/mapnik
Handle large errors in marker placement.
Closes #1485.