Documentation says the limit is 5, but it was really 10 (at least
since 2004).  But since MPD wants to promote using many small clients
idling around, and these clients consume only very few resources, it
seems reasonable to raise this limit's default value.

Similar to c45f1138

Closes https://github.com/MusicPlayerDaemon/MPD/issues/781

Similar to commits e8f2f980 and
ff1ff1e5

Closes https://github.com/MusicPlayerDaemon/MPD/issues/783

Travis has changed the canonical name for this a while ago.

(Now really.  The last commit for this was empty.)

Aparently, libcdio sometimes returns empty filenames, causing MPD
crashes.  This shouldn't really happen, and I consider this a libcdio
bug - but if it happens, people blame MPD, so let's add a check.

Closes https://github.com/MusicPlayerDaemon/MPD/issues/776

Merge some duplicate code in a central library.

Workaround for Travis failures as described in
 https://travis-ci.community/t/macos-build-fails-because-of-homebrew-bundle-unknown-command/7296/18

Travis has changed the canonical name for this a while ago.

Fixes
../src/time/ISO8601.cxx:67:24: error: use of undeclared identifier 'strtoul'
        unsigned long value = strtoul(s, &endptr, 10);
                              ^
../src/time/ISO8601.cxx:77:14: error: use of undeclared identifier 'strtoul'
                        minutes = strtoul(s, &endptr, 10);
                                  ^

on NetBSD with clang 9.0.0.

Using libgme 0.6.2 on macOS, it appears that gme_info_t strings can be
empty, which creates weird track titles: (001/050)

This adds an additional check for an empty string.

Fixes strange C++11 compatibility problems during GTest installation:

 /tmp/gtest-20200216-20679-mu1044/googletest/include/gtest/internal/gtest-internal.h:1249:1: error: unknown type name 'constexpr'
 constexpr bool TypedTestCaseIsDeprecated() { return true; }

 /tmp/gtest-20200216-20679-mu1044/googletest/include/gtest/internal/gtest-internal.h:1249:11: error: expected unqualified-id
 constexpr bool TypedTestCaseIsDeprecated() { return true; }

 /tmp/gtest-20200216-20679-mu1044/googletest/include/gtest/internal/gtest-internal.h:1254:1: error: unknown type name 'constexpr'
 constexpr bool RegisterTypedTestCase_P_IsDeprecated() { return true; }

pip is bugged on arm64 and s390x. Add --no-cache-dir to fix. For
consistency, it doesn't hurt to add everywhere.

"The issue is that ParseCommandArgSignedSongTime parses with
SongTime::FromS, not SignedSongTime::FromS, before casting back to a
SignedSongTime for the return. With x86 overflow rules this doesn't
matter, but on ARM the first cast turns negative values to zero."

Closes https://github.com/MusicPlayerDaemon/MPD/issues/757

This is still needed for GTest 1.8.0 (Travis / Ubuntu Bionic).