* exceptions.cc (interruptible): Allocate slightly more space for directory

name check.  Windows 95 seems to null-terminate the directory otherwise.
(interrupt_on_return): Issue a fatal error if we can't find the caller's stack.
* spawn.cc (find_exec): Accept a path_conv argument rather than a buffer so
that the caller can find things out about a translated path.
(perhaps_suffix): Ditto.
(spawn_guts): Allocate path_conv stuff here so that we can find out stuff about
the translated path (this is work in progress).
* environ.cc (environ_init): Accept an as-yet unused argument indicating
whether we were invoked from a cygwin parent or not.
(winenv): Ditto.
(posify): Accept an argument indicating whether the path has already been
translated.
* dlfcn.cc (check_access): Provide a path_conv buffer to find_exec.
* exec.cc (sexecvpe): Ditto.
* path.cc (path_conv::check): Rename from path_conv::path_conv.
(mount_item::getmntent): Recognize "Cygwin executable" bit.
(symlink_info::check): Remove debugging statements.
* path.h (class path_conv): Add iscygexec method.  Rewrite constructor to call
"check" method to allow multiple operations on a path_conv variable.
* pinfo.cc (pinfo_init): Pass argument to environ_init.
* shared.h: Bump PROC_MAGIC.
* winsup.h: Reflect above changes to function arguments.
* include/sys/mount.h: Add MOUNT_CYGWIN_EXEC type.

winsup/cygwin/shared.h

@@ -187,7 +187,7 @@ pinfo *__stdcall procinfo (int n);
 
 enum
 {
-  PROC_MAGIC = 0xaf05f000,
+  PROC_MAGIC = 0xaf06f000,
   PROC_FORK = PROC_MAGIC + 1,
   PROC_EXEC = PROC_MAGIC + 2,
   PROC_SPAWN = PROC_MAGIC + 3,