Consolidate xc_ptrace and xc_ptrace_core

Consolidate xc_ptrace and xc_ptrace_core

* xc_ptrace
  - Merge xc_ptrace_core into xc_ptrace
  - ATTACH now reads the data argument. If non-zero then
    a corefile is being debuged. Otherwise a thread has
    been attached to. This allows xc_waitdomain_core() or
    xc_waitdomain() to be called as appropriate in
    subsequent xc_ptrace() calls.
* xc_waitdomain
  - Rename xc_waitdomain (xc_ptrace.c version) __xc_waitdomain
  - Rename xc_waitdomain (xc_ptrace_core.c version) xc_waitdomain_core
  - Create xc_waitdomain (in xc_ptrace.c), a wrapper for __xc_waitdomain
    and xc_waitdomain_core.
  Consolidation seemed difficult but ctxt needs to be
  passed into xc_waitdomain_core or made global.
  Alternatively, xc_waitdomain_core could be moved into xc_ptrace.c,
  but this seems messy.
* map_domain_va
  - Rename map_domain_va (xc_ptrace_core.c version) map_domain_va_core
  - Have it accept ctxt, like xc_waitdomain_core
* myptrace and myxcwait (linux-xen-low.c)
  Removed, call the now generic xc_ptrace() and xc_waitdomain() instead

When calling xc_ptrace ATTACH, if a corefile is in use, a fd will
be passed, otherwise a pid. The fd part is important, as this
is saved internally in xc_ptrace_core.c, and passed to xc_waitdomain_core()
as neccessary. Pereviously xc_waitdomain_core() received a pid and
thus could not open the corefile.

Signed-Off-By: Horms <horms@verge.net.au>