Implemented support for working with remote repositories.

libfetch from NetBSD's pkgsrc has been imported into lib/fetch, but
the objects are embedded into libxbps. Only a public function to fetch
files has been implemented: xbps_fetch_file().

The library now is built with -fvisibility=hidden by default, and
exported symbols are the ones that use the SYMEXPORT macro.

The code works well enough, but will need many more cleanups.

--HG--
extra : convert_revision : xtraeme%40gmail.com-20091027004600-0lq9aao67lisbzxv

doc/BINPKG_REPOSITORY

@@ -11,13 +11,8 @@ a "dictionary per package". Additional objects are added into the
 main dictionary to specify more info, like:
 
 	- pkgindex-version: version used to build the index.
-	- location-local: local path to the repository.
-	- location-remote: remote URI repository.
 	- total-pkgs: total of number of available packages.
 
-"location-local" will always be created, and it might be exported via
-a remote location specified with "location-remote".
-
 The package dictionary will be the same than the one available in
 package's metadata directory "/var/db/xbps/metadata/$pkgname/props.plist",
 but some additional objects are added to provide enough info for
@@ -32,10 +27,6 @@ Here's how the package index plist file shall look like in a repository:
 <dict>
 	<key>pkgindex-version</key>
 	<string>1.0</string>
-	<key>location-local</key>
-	<string>/xbps/repo/local</string>
-	<key>location-remote</key>
-	<string>http://www.xbps-remote.org/repo/public</string>
 	<key>total-pkgs</key>
 	<integer>666</integer>
 	<key>available-packages</key>