shelve: remove useless and incorrect code paths for file access This patch removes code paths in "shelvedfile.opener()", because: - explicit "vfs.mkdir()" invocation is useless "vfs.__call__()" for modes other than "read" creates parent directory of target file automatically by "util.ensuredirs()". - mode checking in "except IOError" code path is useless ENOENT occurs only for "read" mode, because target file is created forcibly for other modes. - there is no explicit "return" statement in the code path for "except IOError" if "mode[0] in 'wa'" this is incorrect, because None may be returnd unexpectedly, even though it seems the EEXIST case in the directory creation race for ".hg/shelved" and is very rare. this directory creation race is also treated in "util.ensuredirs()".