Implementation of dependency checking 1

Generate a switch for configuration

BLFS/xsl/gen_config.xsl

@@ -104,6 +104,27 @@ menu    "Build settings"
             set this option to y. Due to the book layout, several scripts
             are not functional in this case. Please review them.
 
+    config	DEP_CHECK
+    bool "Check dependencies of the requested package(s)"
+    default n
+    depends on WRAP_INSTALL
+    help
+      Setting this option does not work if more than one package
+      is selected. It will do the following:
+      - Build the dependency tree and generate a build ordered list
+        disregarding already installed packages
+      - Generate the scripts for the dependencies not already
+        installed (as usual)
+      - Generate a stript that:
+        + removes all unneeded packages using porg
+          (at this point the blfs_tools cannot be used anymore,
+          and your system may be non functional, so use a console
+          for that, not a graphical environment)
+        + installs the package
+        + restores all the previously removed packages
+      Note that this script may not be the last one, if there are runtime
+      dependencies
+
 endmenu
 
 menu "Build Layout"