[stdlib] merge branch! now perform a complete flush before merging by default

Otherwise, events written to the buffer before the merge may only be yielded after the merge is already done; if such an event would lead to the script being interrupted, we would likely want the state not to be merged in the first place, hence the change.

test/results/paragraph run force.ans

@@ -1,17 +0,0 @@
---# run #--
---- text ---
-| {}"Force run checkpoint:" |
-| {}"a" |
-| {}"b" |
---- text ---
-| {}"From checkpoint:" |
-| {}"a" |
-| {}"b" |
---- text ---
-| {}"Force no checkpoint:" |
-| {}"x" |
-| {}"b" |
---- return ---
-()
---# saved #--
-{"f.checkpoint":#p, "f.reached":*{#p:1}, "f.run":3}

test/results/paragraph run from.ans

@@ -10,6 +10,7 @@
 --- text ---
 | {}"Force no checkpoint:" |
 | {}"x" |
+--- text ---
 | {}"b" |
 --- return ---
 ()

test/results/paragraph run.ans

@@ -2,6 +2,7 @@
 --- text ---
 | {}"No checkpoint:" |
 | {}"x" |
+--- text ---
 | {}"b" |
 --- text ---
 | {}"From checkpoint:" |
@@ -10,6 +11,7 @@
 --- text ---
 | {}"Force no checkpoint:" |
 | {}"x" |
+--- text ---
 | {}"b" |
 --- return ---
 ()

test/tests/paragraph run force.ans

@@ -1,14 +0,0 @@
-:f = "f"!script($_)
-	|x
-	#p!checkpoint($_)
-		|a
-	|b
-
-|Force run checkpoint:
-f!from(#p)
-
-|From checkpoint:
-f!
-
-|Force no checkpoint:
-f!from()

test/tests/paragraph run.ans

@@ -11,4 +11,4 @@ f!
 f!
 
 |Force no checkpoint:
-f!from()
+f!from