Make string encoding explitic

Ruby 2.0 enforces explicit string encodings. The char_constant
testcase fails because the internal (SWIG_FromCharPtrAndSize, using
rb_str_new) defaults to ASCII-8BIT while the test-suite file defaults
to the current shell LOCALE setting.

This patch sets the char_constant_runme.rb encoding to ASCII-8BIT.
Merge pull request #117 from kkaempf/ruby-strict-encoding

Make string encoding explitic
Fix Ruby tracking code to use C hash

Patch id #330
  This is a patch to resolve bug #2034216.
  The bug is that the tracking code uses a ruby hash and thus may
  allocate objects (Bignum) while running the GC. This was tolerated in
  1.8 but is invalid (raises an exception) in 1.9.
  The patch uses a C hash (also used by ruby) instead.