po/doc: more security research results

Apart of the fuzzying part, I'm done with what I can do without help.

The "Running po4a on untrusted content" section needs at least a quick glance
from an experimented Perl programmer.

Signed-off-by: intrigeri <intrigeri@boum.org>

doc/plugins/po.mdwn

@@ -281,14 +281,19 @@ an initial goal, and analysing in detail the possible issues.
 
 ##### Locale::Po4a modules
 
-- the modules we want to use have to be checked, as not all are safe
+The modules we want to use have to be checked, as not all are safe
-  (e.g. the LaTeX module's behaviour is changed by commands included
+(e.g. the LaTeX module's behaviour is changed by commands included in
-  in the content); they may use regexps generated from the content; we
+the content); they may use regexps generated from the content.
-  currently only use the `Text` module
+
-- the `Text` module does not run any external program
+`Chooser.pm` only loads the plugin we tell it too: currently, this
-- check that no module is loaded by `Chooser.pm`, when we tell it to
+means the `Text` module only.
-  load the `Text` one
+
-- `nsgmls` is used by `Sgml.pm`
+`Text` module (I checked the CVS version):
+
+- it does not run any external program
+- only `do_paragraph()` builds regexp's that expand untrusted
+  variables; they seem safe to me, but someone more expert than me
+  will need to check. Joey?
 
 ##### Text::WrapI18N
 
@@ -302,6 +307,13 @@ table manipulation tricks could work; overriding
 `Locale::Po4a::Common::wrapi18n` may be easier. I'm no expert at all
 in this field. Joey? [[--intrigeri]]
 
+> Update: Nicolas François suggests we add an option to po4a to
+> disable it. It would do the trick, but only for people running
+> a brand new po4a (probably too late for Lenny). Anyway, this option
+> would have to take effect in a `BEGIN` / `eval` that I'm not
+> familiar with. I can learn and do it, in case no Perl wizard
+> volunteers to provide the po4a patch. [[--intrigeri]]
+
 ##### Term::ReadKey
 
 `Term::ReadKey` is not a hard dependency in our case, *i.e.* po4a
@@ -324,6 +336,10 @@ use in our case, I suggest we define `ENV{COLUMNS}` before loading
 `Locale::Po4a::Common`, just to be on the safe side. Joey?
 [[--intrigeri]]
 
+> Update: adding an option to disable `Text::WrapI18N`, as Nicolas
+> François suggested, would as a bonus disable `Term::ReadKey`
+> as well. [[--intrigeri]]
+
 ### msgmerge
 
 `refreshpofiles()` runs this external program. A po4a developer