Adjust some error messages in `combinat/`

[fchapoton]

Namely, put them into the standard: no capital, no final dot.

Found cases that needed this fix using

git grep -c "Error(.*\.[\"\'].*)" src/sage/combinat/

There remains more to fix, kept for other tickets.

CC: @tscrim @slel @kliem

Component: combinatorics

Keywords: style

Author: Frédéric Chapoton

Branch/Commit: 2dbc25c

Reviewer: Travis Scrimshaw

Issue created by migration from https://trac.sagemath.org/ticket/33367

[fchapoton]

Branch: u/chapoton/33367

[fchapoton]

Commit: 4e8b104

[fchapoton]

New commits:

4e8b104

some work on error messages inside combinat

[fchapoton]

comment:2

purely cosmetic ticket, green bot, so please review

[sagetrac-git]

Changed commit from 4e8b104 to 2dbc25c

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. New commits:

2dbc25c

fix one typo in sine-Gordon

[fchapoton]

Description changed:

--- 
+++ 
@@ -1 +1,9 @@
 namely, put them into the standard : no capital, no final dot
+
+found using
+
+```
+git grep -c "Error(.*\.[\"\'].*)" src/sage/combinat/
+```
+
+There remains more to fix, kept for other tickets.

[slel]

Changed keywords from none to style

[slel]

Description changed:

--- 
+++ 
@@ -1,6 +1,6 @@
-namely, put them into the standard : no capital, no final dot
+Namely, put them into the standard: no capital, no final dot.
 
-found using
+Found cases that needed this fix using
 
 ```
 git grep -c "Error(.*\.[\"\'].*)" src/sage/combinat/

[tscrim]

Reviewer: Travis Scrimshaw

[tscrim]

comment:6

LGTM.

[vbraun]

Changed branch from u/chapoton/33367 to 2dbc25c