No se pudo cargar el subconjunto externo

xmlto hace xmlto no valida: sintaxis documento Fix o utilizar --skip-validación opción de E / S de error: Intento de carga de la red de alerta entidad DTD: no se pudo cargar entidad externa D DocBook XML V4.5 // EN"

Hoy compilar un proyecto que conoce cuándo se produjo este error:

% make prefix=$HOME all doc info
    SUBDIR git-gui
    SUBDIR gitk-git
    SUBDIR templates
/Applications/Xcode.app/Contents/Developer/usr/bin/make -C Documentation all
    GEN doc.dep
    SUBDIR ../
make[2]: `GIT-VERSION-FILE' is up to date.
    SUBDIR ../
make[2]: `GIT-VERSION-FILE' is up to date.
    XMLTO git-add.1
xmlto: /Users/tmartin/src/git-2.19.2/Documentation/git-add.xml does not validate (status 3)
xmlto: Fix document syntax or use --skip-validation option
I/O error : Attempt to load network entity http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd
/Users/tmartin/src/git-2.19.2/Documentation/git-add.xml:2: warning: failed to load external entity "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd"
D DocBook XML V4.5//EN" "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd"
                                                                               ^
I/O error : Attempt to load network entity http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd
warning: failed to load external entity "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd"
validity error : Could not load the external subset "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd"
Document /Users/tmartin/src/git-2.19.2/Documentation/git-add.xml does not validate
make[1]: *** [git-add.1] Error 13
make: *** [doc] Error 2

Según lo mencionado por https://stackoverflow.com/a/18028336/235992, haga lo siguiente:

brew install asciidoc
brew install xmlto
brew install docbook   
brew install docbook-xsl
//最关键一步，要在命令行的描述文件里面添加这个
==> Caveats
To use the DocBook package in your XML toolchain,
you need to add the following to your ~/.bashrc:

export XML_CATALOG_FILES="/usr/local/etc/xml/catalog"