Dpkg::Control::HashCore: Document is_pgp_signed as a public option

Closes: #735975

debian/changelog

@@ -21,6 +21,8 @@ dpkg (1.17.7) UNRELEASED; urgency=low
     «dpkg-parsechangelog --show».
   * Fix bogus message on dependency parse errors in dpkg-checkbuilddeps.
     Closes: #736778
+  * Document is_pgp_signed as a public Dpkg::Control::Hash option.
+    Closes: #735975
 
   [ Updated dpkg translations ]
   * German (Sven Joachim).

scripts/Dpkg/Control/HashCore.pm

@@ -92,6 +92,13 @@ The user friendly name of the information stored in the object. It might
 be used in some error messages or warnings. A default name might be set
 depending on the type.
 
+=item is_pgp_signed
+
+Set by the parser (starting in dpkg 1.17.0) if it finds an OpenPGP
+signature around the control information. Value can be 0 (default)
+or 1, and undef when the option is not supported by the code (in
+versions older than dpkg 1.17.0).
+
 =back
 
 =cut