Support for compiling SNMP MIBs

This is unfortunately unsuited as a plugin due to its dependence on erlc
for compilation. The MIBs must be compiled before an Erlang source.
Add support for excluding erl files
Merge branch 'erlc-excl' of git://github.com/efcasado/erlang.mk
Add package hanoidb to the index
Merge branch 'compile-mibs' of git://github.com/danielwhite/erlang.mk

Fixed a small whitespace issue in the silent output.
Don't try to compile mibs if the mibs/ directory is missing
Add erl_interface for c_src compile and link

Using LDFLAGS, LDLIBS for link
Don't try compile c_src if not exist
Compile all *.c files in c_src and sub dir
Make env.mk delete on distclean

Because env.mk creates a considerable time, then delete it less often.
Add package unicorn to the index
Add package jiffy_v to the index
Merge branch 'c_src_hanling' of git://github.com/nevar/erlang.mk
Enabled the c_src plugin by default
Merge branch 'master' of git://github.com/shizzard/erlang.mk