objspace_dump.c: fix declaration

* ext/objspace/objspace_dump.c (dump_output): fix declaration,
  mkstemp() needs a writable buffer.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43615 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
test_objspace.rb: assertion for temporary file

* test/objspace/test_objspace.rb (TestObjSpace#test_dump_all): add
  assertion for output to temporary file.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43616 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
rbinstall.rb: spec date from VCS

* tool/rbinstall.rb (Gem::Specification.load): obtain spec date from
  VCS for the case using git, RUBY_RELEASE_DATE is the last resort.
  probably fixes [Bug #9085].

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43617 b2dd03c8-39d4-4d8f-98ff-823fe69b080e