Ensure the passfile is used on Windows

Workaround the limitation of lib/pq that cannot use the passfile
keyword and find the default pgpass.conf file on Windows, by setting
the PGPASSFILE environment variable. It parses the file but without
expanding variables in the path given in PGPASSFILE.

sql.go

@@ -30,6 +30,7 @@ import (
 	"errors"
 	"fmt"
 	"github.com/lib/pq"
+	"os"
 	"strings"
 	"time"
 )
@@ -54,7 +55,20 @@ func pgGetVersionNum(db *sql.DB) (int, error) {
 }
 
 func dbOpen(conninfo *ConnInfo) (*pg, error) {
-	connstr := conninfo.String()
+	// Workaround the limitation of lib/pq that cannot use the passfile
+	// keyword and find the default pgpass.conf file on Windows, by setting
+	// the PGPASSFILE environment variable. It parses the file but without
+	// expanding variables in the path given in PGPASSFILE.
+	if passfile, ok := conninfo.Infos["passfile"]; ok {
+		if err := os.Setenv("PGPASSFILE", passfile); err != nil {
+			l.Warnln("could not set PGPASSFILE environment variable:", err)
+		}
+	}
+
+	// lib/pq does not like the passfile keyword either.
+	c := conninfo.Del("passfile")
+
+	connstr := c.String()
 	l.Verbosef("connecting to PostgreSQL with: \"%s\"", connstr)
 	db, err := sql.Open("postgres", connstr)
 	if err != nil {