Make busybox an optional applet

If it's disabled, code shrinks by about 900 bytes:

function                                             old     new   delta
usr_bin                                               10       -     -10
usr_sbin                                              11       -     -11
install_dir                                           20       -     -20
applet_install_loc                                   184       -    -184
run_applet_and_exit                                  686      21    -665
------------------------------------------------------------------------------
(add/remove: 0/4 grow/shrink: 0/1 up/down: 0/-890)           Total: -890 bytes
   text    data     bss     dec     hex filename
 911327     493    7336  919156   e0674 busybox_old
 909848     493    7336  917677   e00ad busybox_unstripped

but busybox executable by itself does not say anything useful:

$ busybox
busybox: applet not found

Based on the patch by Ron Yorston <rmy@pobox.com>

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 12 insertions, 0 deletions

diff --git a/Config.in b/Config.in
index 0a0b5d7cb..3d1870966 100644
--- a/Config.in
+++ b/Config.in
@@ -116,9 +116,21 @@ config FEATURE_COMPRESS_USAGE
           and have very little memory, this might not be a win. Otherwise,
           you probably want this.
 
+config BUSYBOX
+        bool "Include busybox applet"
+        default y
+        help
+          The busybox applet provides general help regarding busybox and
+          allows the included applets to be listed.  It's also required
+          if applet links are to be installed at runtime.
+
+          If you can live without these features disabling this will save
+          some space.
+
 config FEATURE_INSTALLER
         bool "Support --install [-s] to install applet links at runtime"
         default y
+        depends on BUSYBOX
         help
           Enable 'busybox --install [-s]' support. This will allow you to use
           busybox at runtime to create hard links or symlinks for all the