Module search revamp for pkg managers

The search path listed in an import directive can now be an array.  The
top-level search path is appended.  Null and empty strings in the path
terminate any search.  The "." in "." and "./*" is replaced with the
directory containing the file doing the import (for command-line
programs this is the current directory, though that may be a bad idea).

No version numbers or anything of the sort are gratuitously added to the
search paths.

All this makes external package managers possible by allowing
dependencies to be installed local to dependents.

tests/run

@@ -137,12 +137,12 @@ if ! $VALGRIND $Q ./jq -ner -L $mods 'import a as foo; import b as bar; import a
     exit 1
 fi
 
-if ! $VALGRIND $Q ./jq -ner -L $mods 'import c as foo; [foo::a, foo::c] | . == [0,"acmeh"]' > /dev/null; then
+if ! $VALGRIND $Q ./jq -ner -L $mods 'import c as foo; [foo::a, foo::c] | . == [0,"acmehbah"]' > /dev/null; then
     echo "Module system appears to be broken" 1>&2
     exit 1
 fi
 
-if [ "`$VALGRIND $Q ./jq -cner -L $mods '\"c\" | modulemeta'`" != '{"whatever":null,"name":"c","deps":[{"as":"foo","name":"a"},{"search":"$ORIGIN/","as":"d","name":"d"}]}' ]; then
+if [ "`$VALGRIND $Q ./jq -cner -L $mods '\"c\" | modulemeta'`" != '{"whatever":null,"name":"c","deps":[{"as":"foo","name":"a"},{"search":"./","as":"d","name":"d"},{"search":"./","name":"d"},{"search":"./../lib/jq","as":"e","name":"e"},{"search":"./../lib/jq","as":"f","name":"f"}]}' ]; then
     echo "modulemeta builtin appears to be broken" 1>&2
     exit 1
 fi
@@ -171,3 +171,14 @@ if [ -n "$VALGRIND" ] && ! grep 'ERROR SUMMARY: 0 errors from 0 contexts' $d/out
     cat $d/out
     exit 1
 fi
+
+if ! $VALGRIND ./jq -ner -L $mods -f $mods/test_bind_order.jq > $d/out 2>&1; then
+    echo "Import bind order is broken" 1>&2
+    exit 1
+fi
+
+if [ -n "$VALGRIND" ] && ! grep 'ERROR SUMMARY: 0 errors from 0 contexts' $d/out > /dev/null; then
+    echo "Memory errors when programs have syntax errors" 1>&2
+    cat $d/out
+    exit 1
+fi