Fix texinfo 7 dependency on perl

Texinfo 7 depends on perl.
If one does not have perl installed, the following error is raised:

```
INFO checking for perl... /usr/bin/perl
INFO checking Perl version and modules... no
INFO configure: error: perl >= 5.8.1 with Encode and Data::Dumper required by Texinfo.
```

See merge request !1728

component/texinfo/buildout.cfg

 [buildout]
 extends =
   ../ncurses/buildout.cfg
+  ../perl/buildout.cfg
 
 [texinfo]
 # Most other components are not happy with texinfo 5, because it treats some
@@ -28,3 +29,4 @@ configure-options =
 environment =
   CFLAGS=-I${ncurses:location}/include
   LDFLAGS=-L${ncurses:location}/lib -Wl,-rpath=${ncurses:location}/lib
+  PATH=${perl:location}/bin/:%(PATH)s