Makefile cleanup, support for build dirs w/spaces

When I added tvheadend to my jenkins build server I stumbled upon the fact that it doesn't support spaces in the path when attempting to build it.  That was the impetuous for this pull request, although it does some other build/support changes as well:

- support spaces in tvheadend build path in configure, support scripts, and Makefile
- remove references to $(CURDIR) in Makefile, as it's not needed and doesn't help with invoking make from outside the tvheadend dir ($CURDIR is effectively the same as $PWD)
- remove reference to unset Makefile var $(ALLDEPS) from tvheadend linker line
- fix issue with overridden $(BUILDDIR)s in .config.mk: don't require/assume "build.${PLATFORM}"
- fix typo in tvhlog warning message (src/access.c)
- fix typos in html documentation
- error check argument passed into epgdump
- send error messages to stderr in support scripts
- use the same die function for all support scripts