Fix some corner-case bugs in _sendSQLLine's parsing of SQL commands

> found in a pg_dump archive.  It had problems with dollar-quote tags
broken across bufferload boundaries (this may explain bug report from
Rod Taylor), also with dollar-quote literals of the form $a$a$...,
and was also confused about the rules for backslash in double quoted
identifiers (ie, they're not special).  Also put in placeholder support
for E'...' literals --- this will need more work later.

src/bin/pg_dump/pg_backup_archiver.h

@@ -17,7 +17,7 @@
  *
  *
  * IDENTIFICATION
- *		$PostgreSQL: pgsql/src/bin/pg_dump/pg_backup_archiver.h,v 1.66 2005/07/27 12:44:10 neilc Exp $
+ *		$PostgreSQL: pgsql/src/bin/pg_dump/pg_backup_archiver.h,v 1.67 2005/09/11 04:10:25 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -136,22 +136,24 @@ typedef struct _outputContext
 
 typedef enum
 {
-	SQL_SCAN = 0,
-	SQL_IN_SQL_COMMENT,
-	SQL_IN_EXT_COMMENT,
-	SQL_IN_QUOTE,
-	SQL_IN_DOLLARTAG,
-	SQL_IN_DOLLARQUOTE
+	SQL_SCAN = 0,				/* normal */
+	SQL_IN_SQL_COMMENT,			/* -- comment */
+	SQL_IN_EXT_COMMENT,			/* slash-star comment */
+	SQL_IN_SINGLE_QUOTE,		/* '...' literal */
+	SQL_IN_E_QUOTE,				/* E'...' literal */
+	SQL_IN_DOUBLE_QUOTE,		/* "..." identifier */
+	SQL_IN_DOLLAR_TAG,			/* possible dollar-quote starting tag */
+	SQL_IN_DOLLAR_QUOTE			/* body of dollar quote */
 } sqlparseState;
 
 typedef struct
 {
-	int			backSlash;
-	sqlparseState state;
-	char		lastChar;
-	char		quoteChar;
-	int			braceDepth;
-	PQExpBuffer tagBuf;
+	sqlparseState state;		/* see above */
+	char		lastChar;		/* preceding char, or '\0' initially */
+	bool		backSlash;		/* next char is backslash quoted? */
+	int			braceDepth;		/* parenthesis nesting depth */
+	PQExpBuffer tagBuf;			/* dollar quote tag (NULL if not created) */
+	int			minTagEndPos;	/* first possible end position of $-quote */
 } sqlparseInfo;
 
 typedef enum