* ext/dbm/extconf.rb: detect gdbm_version in libgdbm.

	* ext/dbm/dbm.c: make DBM::VERSION more informative for gdbm, qdbm and
	  Berkeley DB 1.x.  [ruby-dev:44944]

	* ext/dbm/dbm.c: use db_version() instead of DB_VERSION_STRING to
	  detect runtime Berkeley DB version.
	  use dpversion instead of _QDBM_VERSION to detect runtime QDBM
	  version.
	  [ruby-dev:44948]

	* ext/dbm/dbm.c (Init_dbm): fix a build error on mswin32.
	  use `extern __declspec(dllimport)` for dll link with VC.
	  [ruby-core:41996] [Bug #5869]


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_1_9_3@34502 b2dd03c8-39d4-4d8f-98ff-823fe69b080e