t0000: catch trivial pilot errors.

People seem to be getting test failure from t6021 not becuase
git is faulty but because they forgot to install "merge".  Check
this and other trivial pilot errors in the first test.

Signed-off-by: Junio C Hamano <junkio@cox.net>

t/t0000-basic.sh

@@ -17,8 +17,37 @@ IDs.  When object ID computation changes, like in the previous case of
 swapping compression and hashing order, the person who is making the
 modification *should* take notice and update the test vectors here.
 '
+
+################################################################
+# It appears that people are getting bitten by not installing
+# 'merge' (usually part of RCS package in binary distributions)
+# or have too old python without subprocess.  Check them and error
+# out before running any tests.  Also catch the bogosity of trying
+# to run tests without building while we are at it.
+
+../git >/dev/null
+if test $? != 1
+then
+	echo >&2 'You do not seem to have built git yet.'
+	exit 1
+fi
+
+merge >/dev/null 2>/dev/null
+if test $? == 127
+then
+	echo >&2 'You do not seem to have "merge" installed.
+Please check INSTALL document.'
+	exit 1
+fi
+
 . ./test-lib.sh
 
+"$PYTHON" -c 'import subprocess' || {
+	echo >&2 'Your python seem to lack "subprocess" module.
+Please check INSTALL document.'
+	exit 1
+}
+
 ################################################################
 # init-db has been done in an empty repository.
 # make sure it is empty.

t/test-lib.sh

@@ -179,18 +179,23 @@ export PATH GIT_EXEC_PATH
 PYTHON=`sed -e '1{
 	s/^#!//
 	q
-}' ../git-merge-recursive` &&
+}' ../git-merge-recursive` || {
+	error "You haven't built things yet, have you?"
+}
 "$PYTHON" -c 'import subprocess' 2>/dev/null || {
 	PYTHONPATH=$(pwd)/../compat
 	export PYTHONPATH
 }
+test -d ../templates/blt || {
+	error "You haven't built things yet, have you?"
+}
 
 # Test repository
 test=trash
 rm -fr "$test"
 mkdir "$test"
 cd "$test"
 "$GIT_EXEC_PATH/git" init-db --template=../../templates/blt/ 2>/dev/null ||
-error "cannot run git init-db"
+error "cannot run git init-db -- have you built things yet?"
 
 mv .git/hooks .git/hooks-disabled