edoc, syntax_tools: Don't fail on invalid UTF-8

As a temporary measure to ease the transition to default UTF-8
encoding, automatically fall back to the Latin-1 encoding (without any
warnings; the Erlang Compiler will emit a proper warning).

The intention is to remove this workaround in OTP 18 or 19.
Prepare release
Merge branch 'maint'
edoc: Fix Map type information for docs
edoc: More Map tests
Merge branch 'maint'
Update version numbers
Update release notes
Merge tag 'OTP-17.3'

=== OTP-17.3 ===

Changed Applications:
- asn1-3.0.2
- common_test-1.8.2
- compiler-5.0.2
- crypto-3.4.1
- dialyzer-2.7.2
- diameter-1.7.1
- edoc-0.7.15
- erl_docgen-0.3.6
- erl_interface-3.7.18
- erts-6.2
- eunit-2.2.8
- hipe-3.11.1
- ic-4.3.6
- inets-5.10.3
- jinterface-1.5.10
- kernel-3.0.3
- megaco-3.17.2
- mnesia-4.12.3
- observer-2.0.2
- odbc-2.10.21
- os_mon-2.3
- ose-1.0.1
- public_key-0.22.1
- sasl-2.4.1
- snmp-5.1
- ssh-3.0.5
- ssl-5.3.6
- stdlib-2.2
- tools-2.7
- wx-1.3.1

Unchanged Applications:
- cosEvent-2.1.15
- cosEventDomain-1.1.14
- cosFileTransfer-1.1.16
- cosNotification-1.1.21
- cosProperty-1.1.17
- cosTime-1.1.14
- cosTransactions-1.2.14
- debugger-4.0.1
- eldap-1.0.3
- et-1.5
- gs-1.5.16
- orber-3.7
- otp_mibs-1.0.9
- parsetools-2.0.11
- percept-0.8.9
- reltool-0.6.6
- runtime_tools-1.8.14
- syntax_tools-1.6.16
- test_server-3.7.1
- typer-0.9.8
- webtool-0.8.10
- xmerl-1.3.7

Conflicts:
	OTP_VERSION
	erts/vsn.mk