Revert commit e0492d4 "Ensure a query is canceled, if a thread is about
to be killed."

This is due to this discussion:
https://groups.google.com/d/topic/ruby-pg/5_ylGmog1S4/discussion

We were using rb_thread_call_without_gvl() with an ubf which canceled
the query currently being processed. This turned out to be incompatible
with possibly registered signal handlers (by Signal.trap).
A ubf is unconditionally invoked if ANY signal fires on a process (eg
even: USR1 or PROF) and Ruby has handlers registered. Cancelling
queries in those conditions does no make sense.

This commit re-enables Connection#async_exec based on the async API
for all ruby versions, because async_exec allowes cancelation of
queries by signals like Control+C.

Thanks to Sam Saffron for highlighting this issue.

--HG--
branch : revert_query_cancel_on_ubf
Add test case for compatibility with signal handlers. See 97c3ec2.

--HG--
branch : revert_query_cancel_on_ubf
Merged in larskanis/ruby-pg/revert_query_cancel_on_ubf (pull request #18)

Revert commit e0492d4 "Ensure a query is canceled, if a thread is about to be killed."
Update History file
Bump the patch version, set the date in History.
Added signature for changeset 22d57e3a2b37
Add column based type mapping.

This allowes to speed up result retrieval by directly converting
integer and float values to proper ruby types.
Don't depend on TYPE(obj)==T_DATA of a proc object for compat with rubinius.
Use instances of PG::ColumnMapping::CConverter as representation of the buildin converters instead of plain symbols. Symbol arguments are converted to these instances, for convenience.

This allows to store and retrieve additional informations to the
conversion and also which conversions are supported.
Add converter BinaryInteger.
Add Boolean ColumnMapping spec and do Integer a bit more compact.
Add convenience method PG::Result#map_types!
Add test case for default_mapping in Result#map_types!
Add test case for all value retrieving methods of PG::Result .
Change ColumnMapping#initialize to take one Array arg rather than a parameter list.

Suggested by Aaron: https://groups.google.com/d/msg/ruby-pg/PE5K6q9RzBs/M5prOno39DEJ
Add BinaryFloat converter.
Add BinaryBolean converter.

Refactor converter tests.
Use old BYTEA escaping for compat with PostgreSQL 8.4
Add compat with Ruby-1.8.7.
Add compat with Windows platform.