Merge remote-tracking branch 'origin/topic/jsiwek/load-sigs'

* origin/topic/jsiwek/load-sigs:
  Add @load-sigs directive for loading signature files (addresses #551).

Closes #551.

scripts/base/frameworks/dpd/main.bro

@@ -3,8 +3,7 @@
 
 module DPD;
 
-## Add the DPD signatures to the signature framework.
-redef signature_files += "base/frameworks/dpd/dpd.sig";
+@load-sigs ./dpd.sig
 
 export {
 	## Add the DPD logging stream identifier.

scripts/base/init-bare.bro

@@ -615,7 +615,9 @@ function add_signature_file(sold: string, snew: string): string
 	}
 
 ## Signature files to read. Use ``redef signature_files  += "foo.sig"`` to
-## extend. Signature files will be searched relative to ``BROPATH``.
+## extend. Signature files added this way will be searched relative to
+## ``BROPATH``.  Using the ``@load-sigs`` directive instead is preferred
+## since that can search paths relative to the current script.
 global signature_files = "" &add_func = add_signature_file;
 
 ## ``p0f`` fingerprint file to use. Will be searched relative to ``BROPATH``.

scripts/base/protocols/http/file-ident.bro

@@ -6,7 +6,8 @@
 @load ./utils
 
 # Add the magic number signatures to the core signature set.
-redef signature_files += "base/protocols/http/file-ident.sig";
+@load-sigs ./file-ident.sig
+
 # Ignore the signatures used to match files
 redef Signatures::ignored_ids += /^matchfile-/;