Force HTTP method name to be uppercase

Ref: Spec: 9.1.3 (1)
http://oauth.net/core/1.0a/#rfc.section.9.1.3
Fix built-in user providers
Merge pull request #324 from stloyd/bugfix/user_providers

[RFC] Fix built-in user providers
Make OAuthUtils::signRequest() compatible with specification
Fix misplaced setting in security docs. Fix #393
Merge pull request #389 from stloyd/bugfix/utils

Make OAuthUtils::signRequest() compatible with specification
Prepare release 0.2.8
Merge branch '0.2'

Conflicts:
	CHANGELOG.md
	Security/Core/User/EntityUserProvider.php
	Security/Core/User/FOSUBUserProvider.php