Add a leak suppression for backtrace_alloc

This appears to be an internal rust thing: I don't know why it's
leaking.  We should investigate further.

src/test/include.am

@@ -364,6 +364,7 @@ EXTRA_DIST += \
 	src/test/fuzz_static_testcases.sh \
 	src/test/slownacl_curve25519.py \
 	src/test/zero_length_keys.sh \
+        src/test/rust_supp.txt \
 	src/test/test_keygen.sh \
 	src/test/test_key_expiration.sh \
 	src/test/test_zero_length_keys.sh \

src/test/rust_supp.txt

@@ -0,0 +1 @@
+leak:backtrace_alloc

src/test/test_rust.sh

@@ -3,6 +3,7 @@
 
 set -e
 
+export LSAN_OPTIONS=suppressions=${abs_top_srcdir}/src/test/rust_supp.txt
 
 for cargo_toml_dir in "${abs_top_srcdir:-../../..}"/src/rust/*; do
     if [ -e "${cargo_toml_dir}/Cargo.toml" ]; then
@@ -16,5 +17,3 @@ for cargo_toml_dir in "${abs_top_srcdir:-../../..}"/src/rust/*; do
 done
 
 exit $exitcode
-
-