Worked around "can not inline" problem.
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.
Partial revert of 3cbd04e to make libzpool work.  Needs review if this is the right approach.
Added option "-D" to wait for debugger attach in child.