[PATCH] Add/fix docs, add a sanity check, make abstract method explicit

[Former user]

The attached patch:

• documents the PostgreSQL ARRAY support and the rowcount property
• adds a fail-fast sanity check to the PGArray constructor so that others waste less time than I did trying to nest PGArray type engines. (It resulted in a not-immediately-obvious error.)
• adds and documents an abstract (NotImplementedError) method on ExecutionContext that is already implicitly there (exists in subclasses and is called by ResultProxy.rowcount)
• fixes a trivial error in a doc comment (method vs. function)

(I file this patch under “documentation” even though there are code changes, since both of them involve clarifying API usage and should not break calling application code that wasn't already broken.)

[Mike Bayer]

looks good, will commit as part of 0.6.0.

[Mike Bayer]

I see the patch is against 0.5. Am adapting to 0.6 but put it in as is for 0.5 in 4a22734eb1d8dd8f18104747eed8f6f909c36740.

[Mike Bayer]

for 0.6 its 943259264f2e8aea2ab40d52ba5f3235269f9c09.

[Mike Bayer]

Removing milestone: 0.6.0 (automated comment)