Preserve generics in MCP reobfuscation

Matches Forge's reobfuscation call in release.py:
    reobfuscate(None, False, True, True, True, False)
mcp/runtime/reobfuscate.py:
    reobfuscate(conffile, reobf_all, keep_lvt, keep_generics, only_client, only_server):
keep_generics corresponds to the --generics command-line flag.

Without this flag, type parameters are lost in the compiled
bytecode. For example, net.minecraftforge.common.Configuration decompile:

    public java.util.Map categories;

after adding --generics, the generics remain:

    public java.util.Map<java.lang.String,net.minecraftforge.common.ConfigCategory> categories;

See also: http://www.angelikalanger.com/GenericsFAQ/FAQSections/ProgrammingIdioms.html#FAQ711

The type information has no runtime effect, but is useful for building mods
against (a remapped version of) MCPC+ as a library, e.g. using SpecialSourceMP.
Casts were needed before this commit because the type info was lost; now they
are no longer needed because the information is preserved, just as in vanilla Forge.