Merge branch '0.3.5-fix-643'
helper: do not strip in string_sanitize

Stripping the string causes leading whitespace on the first line
of a message to be removed leading to weird indentation in thread
view for some html messages.

string_sanitize is also used for mail header parsing but I would
not expect them to contain undesired whitespace too often either.
Merge branch '0.3.5-fix-stringsanitize-644' into testing