Fix ./configure --help hints (incorrectly compiled sentences, duplicate punctuation etc.)

[Bostjan Skufca Jese]

Sample errors:

  --disable-filter-only_root
                          disable filter "only_root". This filter provides
                          This filter passes only messages generated by root..
                          [default=enable]
  --disable-filter-only_tty
                          disable filter "only_tty". This filter provides This
                          filter passes only messages that have a TTY !=
                          none.. [default=enable]
  --disable-filter-only_uid
                          disable filter "only_uid". This filter provides This
                          filter passes only messages that match given UIDs..
                          [default=enable]
  --disable-all-outputs   disables all outputs at once. Use
                          --enable-output-NAME to reenable individual output.
                          [default=enabled]
  --disable-output-devlog disable output "devlog". This output provides This
                          is the default output of Snoopy.. [default=enable]
  --disable-output-devnull
                          disable output "devnull". This output provides Black
                          hole. [default=enable]
  --disable-output-devtty disable output "devtty". This output provides Write
                          to current console via /dev/tty.. [default=enable]
  --disable-output-stderr disable output "stderr". This output provides Write
                          to stderr. [default=enable]
  --disable-output-stdout disable output "stdout". This output provides Write
                          to stdout. [default=enable]
  --enable-output-syslog  enable output "syslog". This output provides
                          WARNING: This output is causing system hangs with
                          SystemD. Do not use it unless you are absolutely
                          certain you know better!. [default=disable]