plugin registry doesn't parse correctly the plugin_dependencies strings

[Guido Amoruso]

Plugin dependecies for each plugin are checked by the plugin registry when trying to load a new plugin: but they are not parsed correctly.

E.g.: if one plugin depends on "dummy==0.2", the plugin registry actually tries to load a plugin named "dummy==0.2", instead of plugin "dummy" at version "0.2".

[Florian Boucault (fboucault)]

Deprecated with new plugin registry.