Accept values that respond to `to_f` in FloatField.

The checking for acceptable FloatField values was verifying that values
fell between -Infinity and Infinity. This worked for any number object,
including BigDecimal in MRI 1.9.2 <= & JRuby. In MRI 1.9.3 >=,
setting a BigDecimal raised a type error.

Since BigDecimal values pack the same way as Float values and their
aren't min/max values for double/float fields in Protocol Buffers, a
simple `respond_to?(:to_f)` call will suffice when checking for
acceptable values.

Closes #90.
Merge pull request #95 from localshred/90_float_field_type_checking

Accept values that respond to `to_f` in FloatField.
Add fallback support for activesupport 2
Merge pull request #98 from crystalcommerce/activesupport-fallback-2-7-stable

Add fallback support for activesupport 2
Bump version 2.7.11
Fix spec
Remove usage of tap
Remove usage of throw
Fix TTIN signal
Fix threading model
Remove last inproc socket in favor of IO pipe
Merge 'upstream/master' into fix_threading_model
Cleanup
Try to reproduce the bad file descriptor error
Fix bad file descriptor error

ZMQ was throwing a "Bad file descriptor" error when many requests are
made in a small time frame. This happened because each request creates a
new zmq context and a new socket within that context. By using a single
ZMQ context for all requests, the error dissappears.
Reconcile with feedback
Merge pull request #100 from devin-c/fix_threading_model

Fix threading model
Merge branch '2-7-stable'
Merge branch 'master' into 2-8-stable
Bump version 2.8.0.beta3