Propagate source font modification time to svg during conversion.  Similar to
what upstream commit 95a470e941d9a20fbdaca51334e8b6b9d93cfae4 did for TTF
files.

Submitted upstream at http://github.com/fontforge/fontforge/pull/2696

--- a/fontforge/svg.c
+++ b/fontforge/svg.c
@@ -27,7 +27,6 @@
 #include "fontforgevw.h"
 #include <unistd.h>
 #include <math.h>
-#include <time.h>
 #include <locale.h>
 #include <utype.h>
 #include <chardata.h>
@@ -62,7 +61,6 @@ static int svg_outfontheader(FILE *file, SplineFont *sf,int layer) {
     BlueData bd;
     char *hash, *hasv, ch;
     int minu, maxu, i;
-    time_t now;
     const char *author = GetAuthor();
 
     memset(&info,0,sizeof(info));
@@ -78,9 +76,8 @@ static int svg_outfontheader(FILE *file, SplineFont *sf,int layer) {
 	fprintf( file, "\n-->\n" );
     }
     fprintf( file, "<svg xmlns=\"http://www.w3.org/2000/svg\" xmlns:xlink=\"http://www.w3.org/1999/xlink\" version=\"1.1\">\n" );
-    time(&now);
     fprintf( file, "<metadata>\nCreated by FontForge %d at %s",
-	    FONTFORGE_VERSIONDATE_RAW, ctime(&now) );
+	    FONTFORGE_VERSIONDATE_RAW, ctime((time_t*)&sf->modificationtime) );
     if ( author!=NULL )
 	fprintf(file," By %s\n", author);
     else
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<div class='path'>path: <a href='/guix/log/?id=a21db79e5252e6a3f6b0a85fe2681022b02f6537'>root</a>/<a href='/guix/log/gnu?id=a21db79e5252e6a3f6b0a85fe2681022b02f6537'>gnu</a>/<a href='/guix/log/gnu/packages?id=a21db79e5252e6a3f6b0a85fe2681022b02f6537'>packages</a>/<a href='/guix/log/gnu/packages/sssd.scm?id=a21db79e5252e6a3f6b0a85fe2681022b02f6537'>sssd.scm</a></div><div class='content'><table class='list nowrap'><tr class='nohover'><th class='left'>Age</th><th class='left'>Commit message (<a href='/guix/log/gnu/packages/sssd.scm?id=a21db79e5252e6a3f6b0a85fe2681022b02f6537&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2017-07-29 01:08:17 +0200'>2017-07-29</span></td><td><a href='/guix/commit/gnu/packages/sssd.scm?id=4f9dd97e658a8ddc1b672de7af0af8b8aaa4749f'>gnu: sssd: Update to 1.15.3.</a><span class='msg-avail'>...</span></td><td>Tobias Geerinckx-Rice</td></tr>
<tr><td><span title='2017-05-16 00:00:03 +0200'>2017-05-16</span></td><td><a href='/guix/commit/gnu/packages/sssd.scm?id=a068300628e9490d7db3f610699ea8c693946e3d'>gnu: bind: Rename variable to 'isc-bind'.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2017-05-15 21:28:29 +0200'>2017-05-15</span></td><td><a href='/guix/commit/gnu/packages/sssd.scm?id=7fe4e556c03289753b1594e257446fb0306c44b7'>gnu: Add sssd.</a><span class='msg-avail'>...</span></td><td>Ricardo Wurmus</td></tr>
<tr><td><span title='2017-05-15 21:26:50 +0200'>2017-05-15</span></td><td><a href='/guix/commit/gnu/packages/sssd.scm?id=dbe874dcbf349b1629a7222db3d7c14241ad5606'>gnu: Add ding-libs.</a><span class='msg-avail'>...</span></td><td>Ricardo Wurmus</td></tr>