[PATCH RFC] help: align description of 'base rev' with reality [issue5488]

[Kim Alvefur]

# HG changeset patch
# User Kim Alvefur <zash at zash.se>
# Date 1488291548 -3600
#      Tue Feb 28 15:19:08 2017 +0100
# Node ID 397c0aa1cd18439d2ce90a68cd5737fb8dafab49
# Parent  a185b903bda3c64678d1f9399bfa0be8d326dbff
help: align description of 'base rev' with reality [issue5488]

The text about revlogs seems to be wrong about -1 being used to indicate
the start of a delta chain. Attempt to correct this.

diff -r a185b903bda3 -r 397c0aa1cd18 mercurial/help/internals/revlogs.txt
--- a/mercurial/help/internals/revlogs.txt	Tue Feb 21 18:22:07 2017 +0100
+++ b/mercurial/help/internals/revlogs.txt	Tue Feb 28 15:19:08 2017 +0100
@@ -108,9 +108,9 @@ 12-15 (4 bytes)
 
 16-19 (4 bytes)
    Base or previous revision this revision's delta was produced against.
-   -1 means this revision holds full text (as opposed to a delta).
-   For generaldelta repos, this is the previous revision in the delta
-   chain. For non-generaldelta repos, this is the base or first
+   This revision holds full text (as opposed to a delta) if it points to
+   itself. For generaldelta repos, this is the previous revision in the
+   delta chain. For non-generaldelta repos, this is the base or first
    revision in the delta chain.
 
 20-23 (4 bytes)