Merged from trunk -r15350:15360

   Merged from trunk -r15350:15360

|15351  |Evaluate conditional USE deps for *DEPEND atoms saved in vdb entries.                     |
|zmedico|                                                                                          |

|15352  |Bug #304981 - Truncate the build log after successful fetch, instead of removing it, so as|
|zmedico|not to interfere with tail -f.                                                            |

|15353  |Prevent CHOST vdb entries from being created for virtual packages.                        |
|zmedico|                                                                                          |

|15354  |Make sure that config._accept_chost() accepts empty CHOST.                                |
|zmedico|                                                                                          |

|15355  |Use config.environ() instead of config.items() when spawning FETCHCOMMAND.                |
|zmedico|                                                                                          |

|15356  |Add a 'trees' parameter to portdbapi.cp_all(). Thanks to Brian Dolbec (dol-sen) for this  |
|zmedico|patch.                                                                                    |

|15357  |Add a BUILD_TIME vdb entry containing the integer number of seconds since the unix Epoch. |
|zmedico|This will be useful for creating package sets that involve comparison of installed        |
|       |packages to binary packages, especially for binhost users. See discussion here:           |
|       |http://archives.gentoo.org/gentoo-portage-dev/msg_d068a8deefd179cc23808bc23f3de200.xml    |

|15358  |Cache BUILD_TIME in vdb_metadata.pickle.                                                  |
|zmedico|                                                                                          |

|15359  |Cache BUILD_TIME in Package.metadata.                                                     |
|zmedico|                                                                                          |

|15360  |Cache BUILD_TIME in $PKGDIR/Packages and inside bindbapi.                                 |
|zmedico|                                                                                          |

svn path=/main/branches/prefix/; revision=15385