include fails with absolute paths

[DavidGamba]

Given a test file:

= Test

[source, adoc]
----
include::include.adoc[]
----

[source, adoc]
----
include::../include.adoc[]
----

[source, adoc]
----
include::/tmp/include.adoc[]
----

and a simple setup:

$ echo hello > include.adoc

$ echo hello > /tmp/include.adoc

$ echo hello > ../include.adoc

rendering fails with the following error:

libasciidoc test.adoc 
Error: Unresolved directive in test.adoc - include::/tmp/include.adoc[]: chdir /Users/davidgamba/test/asciidoc-absolute-vs-relative/tmp: no such file or directory
Unresolved directive in test.adoc - include::/tmp/include.adoc[]: chdir /Users/davidgamba/test/asciidoc-absolute-vs-relative/tmp: no such file or directory