Merged from trunk 8530:8542

   Merged from trunk 8530:8542

   | 8531    | Implement loading of environment.bz2 from binary and         |
   | zmedico | installed packages. For binary packages, it's loaded prior   |
   |         | to pkg_setup(). For installed packages, it's loaded prior to |
   |         | pkg_prerm(). For simplicity, the current implementation will |
   |         | cause the current environment to override *everything* in    |
   |         | the environment that is being processed. In the future, it   |
   |         | should be more selective and only override the parts that    |
   |         | are strictly necessary.                                      |

   | 8532    | Make preprocess_ebuild_env() explicitly filter out FEATURES  |
   | zmedico | since the value for that variable should never come from a   |
   |         | previously saved environment.                                |

   | 8533    | Make save_ebuild_env() filter out lots of variables that     |
   | zmedico | don't need to be saved.                                      |

   | 8534    | Make AA, PF, and WORKDIR readonly.                           |
   | zmedico |                                                              |

   | 8535    | Move LD_PRELOAD and FAKEROOTKEY filtering from               |
   | zmedico | filter_readonly_variables() to save_ebuild_env().            |

   | 8536    | Add some more variables to filter in                         |
   | zmedico | filter_readonly_variables() and save_ebuild_env().           |

   | 8537    | Now that save_ebuild_env() filters variables that could      |
   | zmedico | cause interference, preprocess_ebuild_env() can rely on it   |
   |         | to clean up the environment enough so that anything left can |
   |         | be allowed to override variables or functions from the       |
   |         | current environment.                                         |

   | 8538    | When ${T}/environment is available, do not source the ebuild |
   | zmedico | since that is redundant. This solves bug #46223.             |

   | 8539    | When ROOT != "/" we only want overrides from the calling     |
   | zmedico | environment to apply to the config that's associated with    |
   |         | ROOT != "/", so we wipe out the "backupenv" for the config   |
   |         | that is associated with ROOT == "/" and regenerate it's      |
   |         | incrementals. Thanks to solar for the suggestion.            |

   | 8540    | Don't make variables readonly during the "depend" phase.     |
   | zmedico |                                                              |

   | 8541    | Fix ${EBUILD_PHASE} quoting.                                 |
   | zmedico |                                                              |

   | 8542    | Instead of filtering out all readonly variables, make it     |
   | zmedico | selective so that any readonly variables that are not        |
   |         | explicitly filtered are allowed to be saved.                 |

svn path=/main/branches/prefix/; revision=8588