Store the crawl version in the textdatabases in SAVEDIR and
upgrade the databases when the crawl version changes.

By default crawl checks for a mtime difference on files in DATADIR to see if an
upgrade is required, but guix nulls all file dates,
and crawl would never upgrade saves.

diff -ur a/source/database.cc b/source/database.cc
--- a/source/database.cc	2018-08-09 21:49:26.000000000 -0400
+++ b/source/database.cc	2018-10-07 18:06:41.022445789 -0400
@@ -25,6 +25,7 @@
 #include "syscalls.h"
 #include "threads.h"
 #include "unicode.h"
+#include "version.h"
 
 // TextDB handles dependency checking the db vs text files, creating the
 // db, loading, and destroying the DB.
@@ -55,6 +56,7 @@
     vector<string> _input_files;
     DBM* _db;
     string timestamp;
+    string version;
     TextDB *_parent;
     const char* lang() { return _parent ? Options.lang_name : 0; }
 public:
@@ -163,7 +165,7 @@
 
 TextDB::TextDB(const char* db_name, const char* d</td></tr></table>
<table class='tabs'><tr><td>
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<input type='hidden' name='id' value='418dd6adb5de1bc26ff9bac1cb0dc7822be52112'/><select name='qt'>
<option value='grep'>log msg</option>
<option value='author'>author</option>
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<input class='txt' type='search' size='10' name='q' value=''/>
<input type='submit' value='search'/>
</form>
</td></tr></table>
<div class='content'><div id='summary'>ing(Version::Long) != version)
+        return true;
+
     for (const string &file : _input_files)
     {
         string full_input_path = _directory + file;
@@ -245,7 +253,7 @@
         ts += buf;
     }
 
-    if (no_files && timestamp.empty())
+    if (no_files && timestamp.empty() && version.empty())
     {
         // No point in empty databases, although for simplicity keep ones
         // for disappeared translations for now.
@@ -313,7 +321,10 @@
             _store_text_db(full_input_path, _db);
         }
     }
+
+    string current_version = string(Version::Long);
     _add_entry(_db, "TIMESTAMP", ts);
+    _add_entry(_db, "VERSION", current_version);
 
     dbm_close(_db);
     _db = 0;