dpkg: Split trigger processing types into required, try-queued and try-deferred

Each of these reasons for processing triggers have different requirements
and attributes:

 - The required one, must perform all checks as it is done as part of a
   simple loop to guarantee Pre-Depends satisfiability.
 - The try-deferred one, must not fail on unsatisfiable dependencies, as
   we are doing opportunistic trigger processing, after a normal
   processing queue run.
 - The try-queued one, must perform all checks and fail hard if any
   unsatisfiable scenario occurs.

1 files changed, 2 insertions, 0 deletions

diff --git a/debian/changelog b/debian/changelog
index 409195f0e..a37ad29a2 100644
--- a/debian/changelog
+++ b/debian/changelog
@@ -94,6 +94,8 @@ dpkg (1.19.3) UNRELEASED; urgency=medium
     - dpkg: Switch dependtry from an int to an enum.
     - dpkg: Move dependtry description from deferred_configure() to its
       declaration.
+    - dpkg: Split trigger processing types into required, try-queued and
+      try-deferred.
   * Build system:
     - get-version: Use a format string with printf.
     - run-script: Use $() instead of deprecated ``.