added support for setting response headers within GET requests
reduced number of changes needed for supporting response headers and fixed a bug that caused non response headers query string parameters to be ignored when issueing a non-authenticated request
fixed bugs and even made simpler
limited autoescaping elimination to url_for
removed obsolete escape and unescape methods
remove const_missing
escape header values
Merge branch 'simpler' into url-with-response-headers
memoize these class methods.

no reason to regenerate these arrays multiple times per use
parameters used for special s3 rest resources don't have a value
only one form of memoization is needed
ruby 1.9 fixes
dont create a new array
escape & and  = in query values

needed for response-content-disposition
#url_for supports :query for custom query params

AWS::S3::S3Object#url(:query => {})
AWS::S3::S3Object.url_for(name, bucket, :query => {})
AWS::S3::S3Object.path!(bucket, name, :query => {})
escape ; in query values too
Merge pull request #80 from github/url_for-with-parameters

escaping improvements