should not pop register when value from multiple assignment required
fix ISBLANK() for Visual Studio < 2013 (ref #2658)

Visual Studio versions older than 2013 lack C99's isblank().
Since only ASCII characters are passed to it, implement it
directly without calling the locale-specific isblank().
Merge pull request #2660 from cremno/fix-isblank-for-visual-studio-versions-older-than-2013

fix ISBLANK() for Visual Studio < 2013
Merge branch 'master' of github.com:mruby/mruby
String#[] accepts float.
Merge pull request #2663 from iij/pr-fix-string-utf8-aref

adding mruby-string-utf8 breaks String#[float]