travis: build with patched libcurl

Ubuntu trusty has a bug in curl when using NTLM credentials in a proxy,
dereferencing a null pointer and causing segmentation faults.  Use a
custom-patched version of libcurl that avoids this issue.

(cherry picked from commit f031e20b)

.travis.yml

@@ -37,7 +37,7 @@ addons:
     - valgrind
 
 dist: trusty
-sudo: false
+sudo: true
 osx_image: xcode8.3
 
 matrix:
@@ -64,7 +64,7 @@ matrix:
    - env: COVERITY=1
 
 install:
-  - if [ "$TRAVIS_OS_NAME" = "osx" ]; then ./script/install-deps-${TRAVIS_OS_NAME}.sh; fi
+  - ./script/install-deps-${TRAVIS_OS_NAME}.sh
 
 # Run the Build script and tests
 script:

script/install-deps-linux.sh

+#!/bin/sh
+
+set -x
+
+echo "deb http://libgit2deps.edwardthomson.com trusty libgit2deps" | sudo tee -a /etc/apt/sources.list
+sudo apt-key adv --keyserver pgp.mit.edu --recv 99131CD5
+sudo apt-get update -qq
+sudo apt-get install -y cmake curl libcurl3 libcurl3-gnutls libcurl4-gnutls-dev libssh2-1-dev openssh-client openssh-server valgrind