Fix PostGIS datasource's schema support

[artemp]

My usage of Mapnik uses schemas extensively. I've noticed that the postgis_datasource::envelope() method was throwing errors which caused my renders to fail.

Attached to this ticket will be the quick patch that I made to allow my tiles to render, again.

[artemp]

[springmeyer] Mak, thanks and nice catch. As you obv. saw given the 'TODO', I noticed this problem as well and missed following up on it. Shame this was not caught before release as we don't currently plan on a 0.7.1.

AFAICT the envelope() method has always failed with custom schema's and the workaround has been to manually set the 'extent' so that the call would be skipped. That should still be possible.

Anyway, thanks for the patch, which looks good. Can you imagine other scenarios where we would need to support multiple schemas? I sense proper schema support needs some more thought.

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[springmeyer] Mak, pasting a few of your more complicated queries here that were failing would also be great.

I'm currently maintaining a large test suite that I will add them too. Its planned to add this into the nosetests when I can find time.

[artemp]

[MakKolybabi] Replying to [comment:3 springmeyer]:

Mak, pasting a few of your more complicated queries here that were failing would also be great.

They weren't even really queries, just the names of tables:
{{{


postgis
localhost
gis
gis

sk.mapnik_segments

...

postgis localhost gis gis canada.boundary_provinces ... }}}

[artemp]

[springmeyer] we're going to make a 0.7.1 stable release and will address this issue, so assigning to 0.7.1 milestone

[artemp]

[springmeyer] fixed in r1631, thanks for the patch Mak!