Added new fstat_blk() and fixed fstat64_blk(), to correctly report device size under Mac OS X.

Under Mac OS X, the "stat" family of library functions return "0" as size for block devices
and a specific "stat_blk" family does not exists.  So we need our own versions, which first
call stat() / fstat() / stat64() / fstat64() and then augment the result with the real size
obtained by an appropriate ioctl().
Removed "isa" handling, since Mac OS X doesn't have architecture-specific paths.
Reworked "getexecname()" replacement, since getprogname() does not return full path.
Added userspace implementations of vnode_vid() vnode_getwithid() and vnode_put() to make libzpool work.
Added option "-D" to wait for debugger attach in child.
Added option to selectively wait in ztest child before/after exec and in zdb for GDB to attach.
Fixed help text for gdb attach.  suppress gdb attach status message, if not used.
Added missing libz to libzpool's dependencies.
Defines Are Evil - fixed crash in debug build due to self-assignment of rootdir pointer.
This was caused by zfs_context_userland.h defining getrootdir() as rootdir, in the
intent to directly insert a fixed vnode_t, which backfires when called in a context,
which has a local rootdir variable defined.
replace "if 0" with "ifndef _KERNEL" to correctly fix a warning.

Fixup of commits 3cbd04e and 00f6e7c.
Added userland implementation of rw_lock_held.

This implementation exactly resembles the in-kernel version,
however it is not clear if both have the right semantic.
Cleaned up the stat64 vs stat mess by removing all references to stat64.

Since MacOSX 10.5 (Leopard), the "normal" stat() call family and the associated
stat structure is 64 bit save.  The stat64 calls are deprecated since 10.6.
Added statically linked ztest_static and zdb_static executables to ease debugging.
Fixed a few warnings.
Libzpool: vn_rele  ist not the same as vnode_close.  Userspace should do nothing in vn_rele.

For Kernel space, we should check if the VN_RELE implementation in include/sys/vnode.h in SPL
makes sense.