docs/manual: update documentation about <pkg>_SOURCE, <pkg>_PATCH and <pkg>_EXTRA_DOWNLOADS

This commit updates the Buildroot manual for the variables used to
indicate where to download the source code from:

 - It updates the description of <pkg>_SOURCE to make it clear that
   Buildroot assume that the tarball is hosted at <pkg>_SITE.

 - It updates the description of <pkg>_PATCH to indicate that not only
   file names (assumed to be hosted at <pkg>_SITE) can be used, but
   also full URLs. This allows to match with what the current code is
   doing.

 - It updates the description of <pkg>_EXTRA_DOWNLOADS to also
   indicate that full URLs are now accepted, following the change made
   in the previous commit.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Reviewed-by: Romain Naour <romain.naour@openwide.fr>
Reviewed-by: "Yann E. MORIN" <yann.morin.1998@free.fr>

docs/manual/adding-packages-generic.txt

@@ -204,18 +204,20 @@ information is (assuming the package name is +libfoo+) :
     +LIBFOO_VERSION = cb9d6aa9429e838f0e54faa3d455bcbab5eef057+ +
     +LIBFOO_VERSION = stable+
 
-* +LIBFOO_SOURCE+ may contain the name of the tarball of
+* +LIBFOO_SOURCE+ may contain the name of the tarball of the package,
-  the package. If +HOST_LIBFOO_SOURCE+ is not specified, it
+  which Buildroot will use to download the tarball from
-  defaults to +LIBFOO_SOURCE+. If none are specified, then
+  +LIBFOO_SITE+. If +HOST_LIBFOO_SOURCE+ is not specified, it defaults
-  the value is assumed to be
+  to +LIBFOO_SOURCE+. If none are specified, then the value is assumed
-  +libfoo-$(LIBFOO_VERSION).tar.gz+. +
+  to be +libfoo-$(LIBFOO_VERSION).tar.gz+. +
   Example: +LIBFOO_SOURCE = foobar-$(LIBFOO_VERSION).tar.bz2+
 
 * +LIBFOO_PATCH+ may contain a space-separated list of patch file
-  names, that will be downloaded from the same location as the tarball
+  names, that Buildroot will download and apply to the package source
-  indicated in +LIBFOO_SOURCE+, and then applied to the package source
+  code. If an entry contains +://+, then Buildroot will assume it is a
-  code. If +HOST_LIBFOO_PATCH+ is not specified, it defaults to
+  full URL and download the patch from this location. Otherwise,
-  +LIBFOO_PATCH+. Note that patches that are included in Buildroot
+  Buildroot will assume that the patch should be downloaded from
+  +LIBFOO_SITE+. If +HOST_LIBFOO_PATCH+ is not specified, it defaults
+  to +LIBFOO_PATCH+. Note that patches that are included in Buildroot
   itself use a different mechanism: all files of the form
   +<packagename>-*.patch+ present in the package directory inside
   Buildroot will be applied to the package after extraction (see
@@ -246,10 +248,12 @@ information is (assuming the package name is +libfoo+) :
     +LIBFOO_SITE=/opt/software/libfoo.tar.gz+ +
     +LIBFOO_SITE=$(TOPDIR)/../src/libfoo/+
 
-* +LIBFOO_EXTRA_DOWNLOADS+ lists a number of additional files that
+* +LIBFOO_EXTRA_DOWNLOADS+ is a space-separated list of additional
-  Buildroot should download from +LIBFOO_SITE+ in addition to the main
+  files that Buildroot should download. If an entry contains +://+
-  +LIBFOO_SOURCE+ (which usually is a tarball). Buildroot will not do
+  then Buildroot will assume it is a complete URL and will download
-  anything with those additional files, except download files: it will
+  the file using this URL. Otherwise, Buildroot will assume the file
+  to be downloaded is located at +LIBFOO_SITE+. Buildroot will not do
+  anything with those additional files, except download them: it will
   be up to the package recipe to use them from +$(BR2_DL_DIR)+.
 
 * +LIBFOO_SITE_METHOD+ determines the method used to fetch or copy the