Make the -x option conditionnal for all travis scripts.

.travis/install.sh

@@ -1,6 +1,6 @@
 #!/bin/bash
 
-set -x
+[ -n "$CGAL_DEBUG_TRAVIS" ] && set -x
 DONE=0
 while [ $DONE = 0 ]
 do

.travis/template.txt

@@ -25,7 +25,7 @@ before_script:
 - cd ..
 script: 
 - cd ./.travis
-- bash -x -e ./build_package.sh $PACKAGE
+- if [ -n "$CGAL_DEBUG_TRAVIS" ]; then  bash -x -e ./build_package.sh $PACKAGE; else bash -e ./build_package.sh $PACKAGE; fi
 notifications:
   email:
     on_success: change # default: always

Scripts/developer_scripts/cgal_check_dependencies.sh

@@ -1,6 +1,6 @@
 #This script must be called from the CGAL root.
 set -e
-set -x
+[ -n "$CGAL_DEBUG_TRAVIS" ] && set -x
 while test $# -gt 0
 do
     case "$1" in