git-gui: handle textconv filter on Windows and in development

When developing/testing we run git-gui.sh directly and the makefile
configured variables are not properly set. Configure the new shellpath
accessor to handle this case.

On Windows we may not find the shell so in this case revert to simply
executing the filter command without the shell intermediate.
Signed-off-by: NPat Thoyts <patthoyts@users.sourceforge.net>

git-gui.sh

@@ -139,7 +139,14 @@ if {$_trace >= 0} {
 }
 
 proc shellpath {} {
-	global _shellpath
+	global _shellpath env
+	if {[string match @@* $_shellpath]} {
+		if {[info exists env(SHELL)]} {
+			return $env(SHELL)
+		} else {
+			return /bin/sh
+		}
+	}
 	return $_shellpath
 }
 

lib/blame.tcl

@@ -461,8 +461,13 @@ method _load {jump} {
 	if {$commit eq {}} {
 		if {$do_textconv ne 0} {
 			# Run textconv with sh -c "..." to allow it to
-			# contain command + arguments.
-			set fd [open |[list [shellpath] -c "$textconv \"\$0\"" $path] r]
+			# contain command + arguments. On windows, just
+			# call the filter command.
+			if {![file executable [shellpath]]} {
+				set fd [open |[linsert $textconv end $path] r]
+			} else {
+				set fd [open |[list [shellpath] -c "$textconv \"\$0\"" $path] r]
+			}
 		} else {
 			set fd [open $path r]
 		}