remove unnecessary depedency in test build
need not to initialize ci->err at toplevel
Test for raise in ensure
Merge pull request #1643 from take-cheeze/remove_unnecessary_depedency

Reduce unnecessary mrbgems full test rebuild.
Merge pull request #1644 from carsonmcdonald/testraiseinensure

Test for raise in ensure
tests for "case" expression.
adjust proc->target_class according to surrounding proc->target_class; based on a patch from @Fleurer; close #1627
Merge pull request #1645 from iij/pr-case-expression-test

tests for "case" expression.
Merge branch 'master' into iij