* dcrt0.cc (dll_crt0_0): Call malloc_init and user_shared_initialize_1

	* dcrt0.cc (dll_crt0_0): Call malloc_init and user_shared_initialize_1
	here in case we're dynamically loaded.  Explain why.
	(dll_crt0_1): Call user_shared_initialize_1 from here.
	* mount.cc (is_native_path): New inline function testing for native
	and long Win32 path prefix.
	(is_unc_share): Remove long WIn32 path prefix test.
	(mount_info::create_root_entry): Use PATH_MAX buffer.
	(mount_info::init): Ditto.
	(mount_info::add_item): Test for is_native_path as well.
	* path.cc (normalize_win32_path): Simplify native path prefix code.
	* shared.cc (user_shared_initialize_1): New function taking user
	shared initialization code relying on malloc and cygtls.
	(user_shared_initialize): Move mountinfo initialization to
	user_shared_initialize_1.
	* shared_info.h (user_shared_initialize_1): Declare.
	* syscalls.cc (seteuid32): Call user_shared_initialize_1 after user
	changed.