* dlopen.c (dlopen): Return NULL when name is NULL (suggested by

* dlopen.c (dlopen): Return NULL when name is NULL (suggested by
chrisiasci@aol.com).
* cygwin.din: Add a new, internally used export - _check_for_executable.
* dcrt0.cc (dll_crt0_1): Set _check_for_executable for older binaries.  Pass
user_data to premain functions.
* fhandler.cc (fhandler_disk_file::open): Only check for executable if the
linked program is intereested in the executable bit.
(fhandler_disk_file::check_execable_p): Delete.
* fhandler.h (executable_states): New enumeration of various states of
executable bit caring.
(fhandler_base::set_execable_p): New method.
* fhandler_termios.cc (fhandler_termios::line_edit): Flag when a signal has
been sent to the tty.  Return -1 when this is so.
* fhandler_console.cc (fhandler_console::read): Return -1 when signal sending
character encountered.
* path.cc (path_conv::check): Record when path refers to a disk device.  Move
executable extension check here.
(check_sysfile): Accomodate new EXEC path states.
(has_suffix): Remove.
(next_suffix): Remove.
(class suffix_scan): New clas.
(suffix_scan::has): New method.
(suffix_scan:next): New method.
(symlink_info::check): Use suffix_scan method to control for scanning for
suffixes.
* path.h (path_conv::exec_state): New method.
* perprocess.h: Make "C" friendly.
* include/cygwin/version.h: Define CYGWIN_VERSION_CHECK_FOR_S_IEXEC.  Bump
CYGWIN_VERSION_API_MINOR.
* include/sys/cygwin.h: Change premain declarations.
* winsup.h: Move __cplusplus test to after builtin defines.