FindDocbookXML4.cmake

[Allen Winter]

Howdy,

I discovered that kdelibs4support and kdoctools have a FindDocBookXML4.cmake.
The diff looks like the following.  Can we unify and move into ECM?
I guess the only real question is which minimum version is required to make both happy?

<      set(DocBookXML_FIND_VERSION "4.2")
---
>      set(DocBookXML_FIND_VERSION "4.5")
33,36c54,59
<         share/xml/docbook/schema/dtd/${version}
<         share/xml/docbook/xml-dtd-${version}
<         share/sgml/docbook/xml-dtd-${version}
<         share/xml/docbook/${version}
---
>         ${CMAKE_INSTALL_DATAROOTDIR}/xml/docbook/schema/dtd/${version}
>         ${CMAKE_INSTALL_DATAROOTDIR}/xml/docbook/xml-dtd-${version}
>         ${CMAKE_INSTALL_DATAROOTDIR}/sgml/docbook/xml-dtd-${version}
>         ${CMAKE_INSTALL_DATAROOTDIR}/xml/docbook/${version}
>         #for building on Mac with docbook installed by homebrew
>         opt/docbook/docbook/xml/${version}