fbt_typoff_init: fix an off by one in determining required memory size

This issue would be silent most of the time, but if the requested memory
is a multiple of a page size, then accessing one element beyond the end
would lead to a kernel page fault.
Otherwise, the unlucky last type would just be inaccessible.

Reported by:	glebius
Tested by:	glebius
MFC after:	6 days
libdwarf: anonymous types are expected to have empty type names...

or no type attributes at all.
This is according to DWARF specification.

MFC after:	13 days
fbt_getargdesc: correctly handle types for return probes

MFC after:	6 days
Revert r248639 to fix build failure on head/
dtrace: ensure that we can always catch a process (e.g. when -c is used)

It is not guaranteed that a program has a symbol table entry for main
and thus that it would be possible to set a breakpoint on it.

Reviewed by:	rpaulo
Discussed with:	rpaulo
MFC after:	13 days
post mountroot event after a real/final root is mounted

not every time an intermediate root (including the first devfs) is
mounted.
This is also consistent with waking up via root_mount_complete.

Reviewed by:	jhb
MFC after:	13 days