Partially implement regex_search.

    2013-07-17  Tim Shen  <timshen91@gmail.com>

	* include/bits/regex.h: regex_search.
	* include/bits/regex_grep_matcher.h: _M__search_from_first.
	* include/bits/regex_grep_matcher.tcc: Implement it.
	* testsuite/28_regex/algorithms/regex_search/basic/string_01.cc:
	New.