CI: install Doxygen

[Akim Demaille]

commit 86576c920d448dc744c71b6355eb54a4dd69a2ec
Author: Akim Demaille <address@hidden>
Date:   Sat Sep 15 10:23:44 2018 +0200

    CI: install Doxygen
    
    * .travis.yml: here, so that its tests are not skipped.
    Remove valgrind: it's too expensive on the CI, and asan does the job.

diff --git a/.travis.yml b/.travis.yml
index 22e0c342..856c200c 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -172,17 +172,17 @@ matrix:
 
 before_install:
   - sudo apt-get update -qq
-  - sudo apt-get install -qq autoconf automake autopoint flex gettext graphviz 
help2man m4 texinfo valgrind
+  - sudo apt-get install -qq autoconf automake autopoint doxygen flex gettext 
graphviz help2man m4 texinfo
   - autoconf --version
   - automake --version
   - autopoint --version
+  - doxygen --version
   - flex --version
   - gettext --version
   - dot -V
   - help2man --version
   - m4 --version
   - makeinfo --version
-  - valgrind --version
   - eval "${MATRIX_EVAL}"
 
 script:
@@ -191,5 +191,4 @@ script:
   - make -j2
   - make check                     VERBOSE=1 TESTSUITEFLAGS=-j2 || cat 
tests/testsuite.log
   - make maintainer-check-posix    VERBOSE=1 TESTSUITEFLAGS=-j2 || cat 
tests/testsuite.log
-#  - make maintainer-check-valgrind VERBOSE=1 TESTSUITEFLAGS=-j2 || cat 
tests/testsuite.log
   - make maintainer-check-g++      VERBOSE=1 TESTSUITEFLAGS=-j2 || cat 
tests/testsuite.log