limit support to Rails >= 3.2 and Ruby >= 1.9

#### Removed outdated version-checking conditions
Modules affected:
+ CSV parser
+ asset registration
+ class reloading in development

#### Removed 99% of our custom class reloader in favor of Rails reloading
Note: I removed the code that purges `app/admin` from Rails' `eager_load_paths`
since there were no bad effects of doing so. Only the code that does this for
Rails' `autoload_paths` seems necessary.

#### Gemspec dependencies updated
+ fastercsv removed
+ coffee-rails added
+ sass replaced by sass-rails