(gdb-var-create-regexp): Removed.

(gdb-var-create-regexp): Removed.
(gdb-var-create-handler): Rewritten using JSON parser.
(gdb-propertize-header): Moved earlier.
(gdb-set-header): Removed to avoid duplication.
(gdb-thread-list-handler-custom, gdb-invalidate-disassembly):
Refresh disassembly buffers only after threads list have been
update.
(gdb-threads-header, gdb-registers-header): Per-buffer header line
variables.