Tweak gh-pages-update.sh
Tweak gh-pages-update.sh

This script generates a new gh-pages index.html and copies javadocs
for the release to /javadoc/$VERSION/ and /javadoc/current/.  This
commit makes its detection of whether the gh-pages branch already
exists more robust by using a git plumbing command instead of checking
file existence in the .git directory.  Also fix outdated wording
talking about wikidoc in one of the messages it prints to console.
(cherry picked from commit 16f1fae57d016ef0b29cb76c9b2eeb8f522a2320)

pluradj/titan,amcp/titan,amcp/titan,samanalysis/titan,pluradj/titan,elubow/titan,elubow/titan,dylanht/titan,englishtown/titan,englishtown/titan,banjiewen/titan,CYPP/titan,amcp/titan,CYPP/titan,dylanht/titan,mbrukman/titan,graben1437/titan,CYPP/titan,thinkaurelius/titan,englishtown/titan,thinkaurelius/titan,elubow/titan,dylanht/titan,banjiewen/titan,banjiewen/titan,thinkaurelius/titan,mbrukman/titan,pluradj/titan,dylanht/titan,thinkaurelius/titan,amcp/titan,mbrukman/titan,graben1437/titan,graben1437/titan,elubow/titan,graben1437/titan,CYPP/titan,samanalysis/titan,mbrukman/titan,samanalysis/titan,samanalysis/titan,mbrukman/titan,englishtown/titan,pluradj/titan,banjiewen/titan