bug#29924: 25.3; write-abbrev-file does not preserve abbrev properties

[Allen Li]

Steps:

Create abbrevs_defs file with contents:

  (define-abbrev-table 'python-mode-abbrev-table
    '(
      ("NT" "NamedTuple" nil :count 0 :case-fixed t)
     ))

Load abbrevs_defs.  Write abbrevs with write-abbrev-file

Expected: File contains something like:

  (define-abbrev-table 'python-mode-abbrev-table
    '(
      ("NT" "NamedTuple" nil :count 0 :case-fixed t)
     ))

Actual:  :case-fixed is missing:

  (define-abbrev-table 'python-mode-abbrev-table
    '(
      ("NT" "NamedTuple" nil 0)
     ))

In GNU Emacs 25.3.1 (x86_64-pc-linux-gnu, GTK+ Version 3.22.26)
 of 2017-12-04 built on arojas
Windowing system distributor 'The X.Org Foundation', version 11.0.11905000
Configured using:
 'configure --prefix=/usr --sysconfdir=/etc --libexecdir=/usr/lib
 --localstatedir=/var --with-x-toolkit=gtk3 --with-xft --with-modules
 'CFLAGS=-march=x86-64 -mtune=generic -O2 -pipe -fstack-protector-strong
 -fno-plt' CPPFLAGS=-D_FORTIFY_SOURCE=2
 LDFLAGS=-Wl,-O1,--sort-common,--as-needed,-z,relro,-z,now'