tool/bisect: add some magic to make the bisect tool be useable when its not part of a checkout

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

.gitignore

@@ -47,6 +47,7 @@
 /tests/videogen
 /tests/vsynth1/
 /tools/aviocat
+/tools/ffbisect
 /tools/cws2fws
 /tools/ffeval
 /tools/graph2dot

tools/bisect

@@ -2,6 +2,23 @@
 
 set -e
 
+if test "bisect" = "`basename $0`" ; then
+    echo WARNING, trying to execute tools/bisect directly this cannot work as
+    echo the script itself would not be available in older checkouts
+    echo please use tools/ffbisect
+    git show master:tools/bisect > tools/ffbisect
+    chmod u+x tools/ffbisect
+    exit 1
+fi
+
+if ! git show master:tools/bisect | diff - tools/ffbisect > /dev/null ; then
+    echo updating tools/ffbisect script to HEAD.
+    git show master:tools/bisect > tools/ffbisect
+    chmod u+x tools/ffbisect
+    tools/ffbisect $*
+    exit 0
+fi
+
 case "$1" in
     need)
         case $2 in