build-sys: sensible errors when autogen.sh requirements are is missing

build-sys: sensible errors when autogen.sh requirements are is missing

<quote="Jim">
I tested the build on several "new" linux installs that didn't yet have any
development tools beyond gcc. On those systems the following error messages
were received:

  ./autogen.sh: line 46: libtoolize: command not found
  ./autogen.sh: line 47: test: =: unary operator expected
</quote>

This commit also removes few unnecessary empty lines, and makes all shell
variables to be wrote in caps & quoted properly.

Cc: Jim Warner <james.warner@comcast.net>
Signed-off-by: Sami Kerola <kerolasa@iki.fi>