Introduce FEATURE_EXEC_PREFER_APPLETS = "re-execute our own

executable if we asked to exec someting with argv[0] == known_applet"
Use it in init. Also respect PATH in init, remove explicit "/sbin" etc
from exec. Patch by Gabriel L. Somlo <somlo@cmu.edu>

scripts/defconfig

@@ -27,6 +27,7 @@ CONFIG_FEATURE_SYSLOG=y
 CONFIG_FEATURE_SUID_CONFIG=y
 CONFIG_FEATURE_SUID_CONFIG_QUIET=y
 # CONFIG_SELINUX is not set
+#CONFIG_FEATURE_EXEC_PREFER_APPLETS is not set
 CONFIG_BUSYBOX_EXEC_PATH="/proc/self/exe"
 
 #