Bash syntax change and comments
Removed another trace to unused "USE flags" and improved info action
Several style (bash-only) changes
Fixed and improved package file lookup

There's now a new function pkgbox_find_package() which tries to find the
desired package file by extracting info from the user-provided "package
string" and searching for the file in common directories.

The rule is as follows:
  1) If package string is already an existing file, then use it
  2) Try ${PKGDIR}/${category}/${l_pn}/${l_p}.pkgbox
  3) Try ${PKGDIR}/${category}/${l_pn}/${l_pn}.pkgbox
  4) Try ${PKGDIR}/${l_pn}/${l_p}.pkgbox
  5) Try ${PKGDIR}/${l_pn}/${l_pn}.pkgbox
  6) Try ${PKGDIR}/${l_p}.pkgbox
  7) Try ${PKGDIR}/${l_pn}.pkgbox
  X) Not found, fail

This fixes the first implementation of 7eb5e22b.
Use more readable form for setting bash options
Use of Bash option "nounset" (-u) for more robust runtime behavior

The "nounset" option requires all variables to be already set (~declared)
before any parameter expansion (~access) happens. Accessing an unset
variable results in an error.

See: <http://www.gnu.org/software/bash/manual/html_node/The-Set-Builtin.html>
Fixed non-functional option -q (quiet) and improved help message
Display pkgbox API-version in package info and made fields optional
Output package info not as system message but info screen
Support for setting the terminal emulator icon name / window title
Info output in pkgVer() about effectively used version
Moved pkgbox directories WORKDIR (work) und T (temp)
Action "info" is now the default action if only package string given
Use Bash arithmetic for verbosity counter

However, due to the use of Bash option errexit we need to modify the
return status in case of non-zero.
Changed verbosity level of several messages