Fix checking return value of fread()
Merge pull request #1501 from iij/pr_fix_read_debug_section

Fix checking return value of fread()
fix syntax error on Heredoc in expression expansion
this works same as CRuby
Merge branch 'heredoc-in-heredoc-2' of github.com:FUKUZAWA-Tadashi/mruby into heredoc-in-heredoc-2