Merge #10657: Utils: Improvements to ECDSA key-handling code

63179d0 Scope the ECDSA constant sizes to CPubKey / CKey classes (Jack Grigg)
1ce9f0a Ensure that ECDSA constant sizes are correctly-sized (Jack Grigg)
48abe78 Remove redundant `= 0` initialisations (Jack Grigg)
17fa391 Specify ECDSA constant sizes as constants (Jack Grigg)
e4a1086 Update Debian copyright list (Jack Grigg)
e181dbe Add comments (Jack Grigg)
a3603ac Fix potential overflows in ECDSA DER parsers (Jack Grigg)

Pull request description:

  Mostly trivial, but includes fixes to potential overflows in the ECDSA DER parsers.

  Cherry-picked from Zcash PR https://github.com/zcash/zcash/pull/2335

Tree-SHA512: 8fcbd51b0bd6723e5d33fa5d592f7cb68ed182796a9b837ecc8217991ad69d6c970258617dc00eb378c8caa4cec5d6b304d9d2c066acd40cda98e4da68e0caa4

contrib/debian/copyright

@@ -15,6 +15,14 @@ Copyright: 2010-2011, Jonas Smedegaard <dr@jones.dk>
            2011, Matt Corallo <matt@bluematt.me>
 License: GPL-2+
 
+Files: src/secp256k1/build-aux/m4/ax_jni_include_dir.m4
+Copyright: 2008 Don Anderson <dda@sleepycat.com>
+License: GNU-All-permissive-License
+
+Files: src/secp256k1/build-aux/m4/ax_prog_cc_for_build.m4
+Copyright: 2008 Paolo Bonzini <bonzini@gnu.org>
+License: GNU-All-permissive-License
+
 Files: src/qt/res/icons/add.png
        src/qt/res/icons/address-book.png
        src/qt/res/icons/chevron.png
@@ -106,6 +114,12 @@ License: Expat
  TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
  SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 
+License: GNU-All-permissive-License
+ Copying and distribution of this file, with or without modification, are
+ permitted in any medium without royalty provided the copyright notice
+ and this notice are preserved. This file is offered as-is, without any
+ warranty.
+
 License: GPL-2+
  This program is free software; you can redistribute it and/or modify it
  under the terms of the GNU General Public License as published by the