Use `bool' (not int) as the type for a few

Use `bool' (not int) as the type for a few
global variables.
(collapse_escapes): Rewrite to set globals rather than modifying
its parameter.
Use size_t (not int) for all counters and related index variables.
(paste_parallel): Remove needless complexity of
using xrealloc in the loop;  just allocate the buffers up front.
Free the two temporary buffers.
Move declarations of locals `down' into scope where used.
(paste_serial): Remove `register' attributes.
(main): Simplify delim-related code.
Free `delims', now that it's malloc'd.