Add experimental support for Inno Setup <1.2.10

This is based entirely on the Inno Setup 1.2 changelog:
 http://www.jrsoftware.org/files/is1.2-whatsnew.htm

No versions were tested due to lack of available installers.

src/setup/file.cpp

@@ -130,8 +130,12 @@ void file_entry::load(std::istream & is, const version & version) {
 	}
 	flagreader.add(CompareTimeStamp);
 	flagreader.add(FontIsNotTrueType);
-	flagreader.add(SkipIfSourceDoesntExist);
-	flagreader.add(OverwriteReadOnly);
+	if(version >= INNO_VERSION(1, 2, 5)) {
+		flagreader.add(SkipIfSourceDoesntExist);
+	}
+	if(version >= INNO_VERSION(1, 2, 6)) {
+		flagreader.add(OverwriteReadOnly);
+	}
 	if(version >= INNO_VERSION(1, 3, 21)) {
 		flagreader.add(OverwriteSameVersion);
 		flagreader.add(CustomDestName);

src/setup/header.cpp

@@ -525,8 +525,12 @@ void header::load(std::istream & is, const version & version) {
 		flagreader.add(DisableAppendDir);
 	}
 	flagreader.add(Password);
-	flagreader.add(AllowRootDirectory);
-	flagreader.add(DisableFinishedPage);
+	if(version >= INNO_VERSION(1, 2, 6)) {
+		flagreader.add(AllowRootDirectory);
+	}
+	if(version >= INNO_VERSION(1, 2, 14)) {
+		flagreader.add(DisableFinishedPage);
+	}
 	if(version.bits() != 16) {
 		if(version < INNO_VERSION(3, 0, 4)) {
 			flagreader.add(AdminPrivilegesRequired);

src/setup/registry.cpp

@@ -111,7 +111,9 @@ void registry_entry::load(std::istream & is, const version & version) {
 	flagreader.add(UninsClearValue);
 	flagreader.add(UninsDeleteEntireKey);
 	flagreader.add(UninsDeleteEntireKeyIfEmpty);
-	flagreader.add(PreserveStringType);
+	if(version >= INNO_VERSION(1, 2, 6)) {
+		flagreader.add(PreserveStringType);
+	}
 	if(version >= INNO_VERSION(1, 3, 9)) {
 		flagreader.add(DeleteKey);
 		flagreader.add(DeleteValue);