fix(signatures): match the guard against on-disk text, newline and all

The guard compared the buffer block, with trailing blank lines trimmed,
against knownSignatures() values returned verbatim by text(), which carry
the trailing newline every editor writes. The two never compared equal, so
a signature read back from disk was always treated as unknown: switching
appended a second signature instead of replacing, and None removed nothing.

Normalise each known entry the same way the block scan does, once in
replace(), rather than per comparison.

Part of item 152.

0 files changed, 0 insertions, 0 deletions