scripts/functions: add a generic custom location infrastructure

Add a generic custom location infrastructure (inspired by the one in
kernel/linux) to allow the user to use custom tarballs or directories
for any component.

Signed-off-by: "David Holsgrove" <david.holsgrove@xilinx.com>
[yann.morin.1998@free.fr: move config option, improve help text, fix API doc]
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Message-Id: <131c163c69f9cc81d2be.1349931191@localhost.localdomain>
PatchWork-Id: 190784
Message-Id: <0bbaba9190a76ba97f72.1349931192@localhost.localdomain>
PatchWork-Id: 190785

diff -dur strace-4.5.15.orig/net.c strace-4.5.15/net.c

--- strace-4.5.15.orig/net.c	2006-12-13 20:57:23.000000000 +0100

+++ strace-4.5.15/net.c	2007-07-14 19:29:36.000000000 +0200

@@ -800,8 +800,12 @@

 #ifdef SOL_PACKET

 static const struct xlat sockpacketoptions[] = {

+#if defined(PACKET_ADD_MEMBERSHIP)

 	{ PACKET_ADD_MEMBERSHIP,	"PACKET_ADD_MEMBERSHIP"	},

+#endif

+#if defined(PACKET_DROP_MEMBERSHIP)

 	{ PACKET_DROP_MEMBERSHIP,	"PACKET_DROP_MEMBERSHIP"},

+#endif

 #if defined(PACKET_RECV_OUTPUT)

 	{ PACKET_RECV_OUTPUT,		"PACKET_RECV_OUTPUT"	},

 #endif