p4a: use subshells for build

distribute.sh.patch

diff --git a/distribute.sh b/distribute.sh
index e891d66..2c3b0e6 100755
--- a/distribute.sh
+++ b/distribute.sh
@@ -6,6 +6,9 @@
 #
 #------------------------------------------------------------------------------
 
+# Automatically export all variables/functions for subshells
+set -a
+
 MODULES=$(cat `dirname $0`/modules)
 
 # Resolve Python path
@@ -672,7 +675,7 @@ function run_build() {
                if [ "X$DO_BUILD" == "X1" ] || [ ! -f "$MARKER_FN" ]; then
                        debug "Call $fn"
                        rm -f "$MARKER_FN"
-                       $fn
+                       try bash -c "$fn"
                        touch "$MARKER_FN"
                else
                        debug "Skipped $fn"