Remove hard-wired lists of timezone abbreviations in favor of providing

configuration files that can be altered by a DBA.  The australian_timezones
GUC setting disappears, replaced by a timezone_abbreviations setting (set this
to 'Australia' to get the effect of australian_timezones).  The list of zone
names defined by default has undergone a bit of cleanup, too.  Documentation
still needs some work --- in particular, should we fix Table B-4, or just get
rid of it?  Joachim Wieland, with some editorializing by moi.

src/include/utils/tzparser.h

@@ -0,0 +1,35 @@
+/*-------------------------------------------------------------------------
+ *
+ * tzparser.h
+ *	  Timezone offset file parsing definitions.
+ *
+ * Portions Copyright (c) 1996-2006, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * $PostgreSQL: pgsql/src/include/utils/tzparser.h,v 1.1 2006/07/25 03:51:22 tgl Exp $
+ *
+ *-------------------------------------------------------------------------
+ */
+#ifndef TZPARSER_H
+#define TZPARSER_H
+
+/*
+ * The result of parsing a timezone configuration file is an array of
+ * these structs, in order by abbrev.  We export this because datetime.c
+ * needs it.
+ */
+typedef struct tzEntry
+{
+	/* the actual data: TZ abbrev (downcased), offset, DST flag */
+	char *abbrev;
+	int offset;					/* in seconds from UTC */
+	bool is_dst;
+	/* source information (for error messages) */
+	int lineno;
+	const char *filename;
+} tzEntry;
+
+
+extern bool load_tzoffsets(const char *filename, bool doit, int elevel);
+
+#endif /* TZPARSER_H */