Extract #!/usr/bin/env interpreter dependencies, part 1 (ticket #136)

Extract #!/usr/bin/env interpreter dependencies, part 1 (ticket #136)
- With "#!/usr/bin/env <interpreter>" shebang directives, rpm previously
  only added a dependency for /usr/bin/env, completely missing the
  actual interpreter. If the interpreter happens to be an absolute path, we
  can just add it as is.
- Patch originally from Ville Skyttä