libxml2-dev does not correctly update the Include path

libxml2 isn't, as far as I know, supposed to be accessed like that. What program is this?

If it's your code, you should compile it with
gcc `xml2-config --cflags` -o foo foo.c

xml2-config is a script that creates the correct cflags for you (in a similar way to how
pkg-config creates glib flags). If this is not your code, there's in all probability a ./configure
script of some sort that needs to be run. I would expect that even if you change your #include's
to <libxml2/libxml/foo.h>, it still won't work.

I may be wrong, but at least this is my understanding of the matter. I found some
information here : http://xmlsoft.org/FAQ.html#Compilatio

Actually, I think it's
gcc `xml2-config --cflags --libs` -o foo foo.c

Here's the output of "cat /usr/lib/pkgconfig/libxml-2.0.pc":
prefix=/usr
exec_prefix=${prefix}
libdir=${exec_prefix}/lib
includedir=${prefix}/include
modules=1

Name: libXML
Version: 2.7.5
Description: libXML library version2.
Requires:
Libs: -L${libdir} -lxml2
Libs.private: -lz -lm
Cflags: -I${includedir}/libxml2

You're supposed to use it with:
AC_CHECK_LIB([xml2], [xmlParseFile])
PKG_CHECK_MODULES(XML2, "libxml-2.0")
in your configure.ac file...

Per comment #1, should be using xml2-config.