Retrieve ruby core source files.

This can be used by any C extension gem that needs Ruby core headers (*.h and *.inc)

Usage:

Ruby_core_source::create_makefile_with_core(hdr_check_proc, gem_name)

takes the place of

create_makefile(gem_name)

in your extconf.rb

This will:

If hdr_check_proc is true, call create_makefile(gem_name)

Else: if core headers already exist, and hdr_check_proc is true, call create_makefile(gem_name)

Else: fetch and extract the core headers, check hdr_check_proc, and call create_makefile(gem_name)

Else: return false

Note that for Ruby preview releases, the corresponding RUBY_REVISION needs to be maintained in

http://cloud.github.com/downloads/mark-moseley/ruby_core_source/preview_revision.yml

Example use in extconf.rb:

require 'ruby_core_source'

hdrs = proc { have_header("vm_core.h") and have_header("iseq.h") }

dir_config("ruby") # allow user to pass in non-standard core include directory

if !Ruby_core_source::create_makefile_with_core(hdrs, "foo")

# error

exit(1)

end