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Always open files in binary mode and handle CRLF <-> LF conversion ourselves
This fixes some problems with READPOS and with reading UTF-16LE.

Merge in change from trunk, mostly to get new tests for LOAD

Add tests for LOAD
- Use LOAD to successfully load a file.
- LOAD a file that defines a STARTUP

Extend LOADTEST to test that line breaks are preserved in procedure definitions.

Change TESTUI to run the test with TRACEINSTRUCTION
This handles when the test outputs something and also prints what test was run.

Refactor FILETEST.OPENREAD.UTF16LE to use WRITEBINARYDATA.
This makes the test more readable.

Add a test for the handling of end-of-line sequences in UTF-16.

Add test coverage for BOM-sniffing and zero byte files

Fix read_char_utf16le to correctly restore the position when mapping CRLF -> LF fails.

Refactoring: move seeking logic for "r+" and "a" modes from open_file to open_helper
open_helper is a better place for this logic because it already has special logic for each OPEN* mode.
This also eliminates some unnecessary seeking.