do not fail the travis build if Python debug packages are missing

.travis.yml

@@ -15,12 +15,14 @@ branches:
 
 before_install:
   - sudo apt-get update
-  - sudo apt-get install gdb python`python -c 'import sys; print("%d.%d" % sys.version_info[:2])'`-dbg
-  - dpkg -l | grep gdb
+  - sudo apt-get install gdb python$((python -c 'import sys; print("%d.%d" % sys.version_info[:2])'))-dbg || true
+  - dpkg -l | grep gdb || true
 
 install: pip install .
 
-script: CFLAGS="-O0 -ggdb" python runtests.py -vv
+script:
+  - PYTHON="`python$((python -c 'import sys; print("%d.%d" % sys.version_info[:2])'))-dbg`"
+  - CFLAGS="-O0 -ggdb" $(($PYTHON -V >/dev/null && echo $PYTHON || echo python)) runtests.py -vv
 
 matrix:
   allow_failures: