fixes #712. c.f. [ruby-dev:37516].

* lib/erb.rb (ERB::Compiler#compile): recognizes magic comments.
  returns a pair of compiled script and its script encoding.

* lib/erb.rb (ERB#set_eoutvar): make generated scripts return a
  string in correct encoding.

* lib/erb.rb (ERB#def_method): use Kernel#eval for encoding-awareness
  of the evaluated string.

* bin/erb.rb (ERB::Main.run): adds -E and -U options.
  String is no longer Enumerable.

* man/erb.1: new manapage.

* test/erb/test_erb_m17n.rb: new test case for m17n features.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@21170 b2dd03c8-39d4-4d8f-98ff-823fe69b080e