Add checks for programs which are required for the test suite to run.

All prerequisite programs are checked for existance, and if any are
missing,
a list of missing programs is printed, and the test suite is aborted.
All programs currently used in the tests, except those in core-utils,
are checked.

tests/run-tests

@@ -104,6 +104,27 b' run_one() {'
     return $fail
 }
 
+# list of prerequisite programs 
+# stuff from coreutils (cat, rm, etc) are not tested
+prereqs="python merge diff grep unzip md5sum gunzip sed"
+missing=''
+for pre in $prereqs ; do
+    if type $pre > /dev/null 2>&1 ; then
+        : prereq exists
+    else 
+        missing="$pre $missing"
+    fi
+done
+
+if [ "$missing" != ''  ] ; then
+    echo "ERROR: the test suite needs some programs to execute correctly."
+    echo "The following programs are missing: "
+    for pre in $missing; do
+        echo "   $pre"
+    done
+    exit 1
+fi
+
 TESTS="$*"
 if [ -z "$TESTS" ] ; then
     TESTS=`ls test-* | grep -v "[.~]"`