`source` doesn't work for some /bin/sh, use `.` instead

tests/test-convert-bzr

@@ -1,6 +1,6 b''
 #!/bin/sh
 
-source "$TESTDIR/bzr-definitions"
+. "$TESTDIR/bzr-definitions"
 
 echo % create and rename on the same file in the same step
 mkdir test-createandrename

tests/test-convert-bzr-directories

@@ -1,6 +1,6 b''
 #!/bin/sh
 
-source "$TESTDIR/bzr-definitions"
+. "$TESTDIR/bzr-definitions"
 
 echo % empty directory
 mkdir test-empty

tests/test-convert-bzr-ghosts

@@ -1,6 +1,6 b''
 #!/bin/sh
 
-source "$TESTDIR/bzr-definitions"
+. "$TESTDIR/bzr-definitions"
 
 cat > ghostcreator.py <<EOF
 import sys

tests/test-convert-bzr-merges

@@ -1,6 +1,6 b''
 #!/bin/sh
 
-source "$TESTDIR/bzr-definitions"
+. "$TESTDIR/bzr-definitions"
 
 echo % test multiple merges at once
 mkdir test-multimerge

tests/test-convert-bzr-treeroot

@@ -1,6 +1,6 b''
 #!/bin/sh
 
-source "$TESTDIR/bzr-definitions"
+. "$TESTDIR/bzr-definitions"
 
 cat > treeset.py <<EOF
 import sys