ash: optional bash-like pattern subst and substring opts

(by James Simmons <jsimmons AT infradead.org>)
TODO: write testsuite!

BASH_COMPAT off:
scanleft                                             101     262    +161
subevalvar                                           346     335     -11
BASH_COMPAT on:
subevalvar                                           346    1397   +1051
scanleft                                             101     262    +161
readtoken1                                          2739    2807     +68
cmdputs                                              397     399      +2
static.vstype                                         64      48     -16
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 4/1 up/down: 1282/-16)         Total: 1266 bytes

1 files changed, 7 insertions, 0 deletions

diff --git a/shell/Config.in b/shell/Config.in
index 9328c9102..5ea071c36 100644
--- a/shell/Config.in
+++ b/shell/Config.in
@@ -47,6 +47,13 @@ config ASH
 comment "Ash Shell Options"
         depends on ASH
 
+config ASH_BASH_COMPAT
+        bool "bash-compatible extensions"
+        default y
+        depends on ASH
+        help
+          Enable bash-conpatible extensions.
+
 config ASH_JOB_CONTROL
         bool "Job control"
         default y