string.c: shrink too big buffer

* string.c (rb_str_resize): shrink the buffer even if new length
  is same but it is enough smaller than the capacity.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@46408 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

Conflicts:
	string.c
file.c: shrink expanded path

* file.c (expand_path): shrink expanded path which no longer needs
  rooms to append.  [ruby-core:63114] [Bug #9934]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@46410 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

Conflicts:
	ChangeLog
string.c: consider capacity

* string.c (rb_str_resize): should consider the capacity instead
  of the old length, as pointed out by nagachika.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@46413 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

Conflicts:
	ChangeLog
add more test coverage for [ruby-core:63136] [Bug #9934]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@46414 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
Merge pull request #18 from github/2.1-expandpath

Backport file_expand memory usage fix