versions not case-insensitive

[cweiske]

Pyrus should automatically uppercase "RC" version numbers when they are given on the command line.

Currently it simply fails:

$ pyrus upgrade pear/php_codesniffer-1.5.0rc3
Pyrus version 2.0.0a4 SHA-1: 72271D92C3AA1FA96DF9606CD538868544609A52
Using PEAR installation found at /opt/phpfarm/inst/php-5.3.27/pear
Pyrus\HTTPException: Download of http://pear.php.net/rest/r/php_codesniffer/v2.1.5.0rc3.xml failed, file does not exist

When using RC3 instead of rc3, it works better.