Add missing #[inline] to methods related to char and fix related problem in String::push

[pmarcelll]

Various methods in both libcore/char.rs and librustc_unicode/char.rs were previously marked with #[inline], now every method is marked in char's impl blocks.
Partially fixes #26124.
EDIT: I'm not familiar with pull reqests (yet), apparently Github added my second commit to thit PR...
Fixes #26124

[rust-highfive]

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[brson]

@bors r+

[bors]

📌 Commit c5d0e2a has been approved by brson

[pmarcelll]

@SimonSapin, since you are the original author of the modified code, could you please look at the second commit to see if there's anything wrong with it? 😃

[Gankra]

@bors r+

[bors]

📌 Commit e87c62f has been approved by Gankro

[Gankra]

Thanks!

[SimonSapin]

@pmarcelll I am? Anyway, looks good to me.

[bors]

⌛ Testing commit e87c62f with merge 34928d9...

[bors]

💔 Test failed - auto-mac-64-nopt-t

[alexcrichton]

@bors: retry

On Wed, Jun 10, 2015 at 7:08 AM, bors notifications@github.com wrote:

[image: 💔] Test failed - auto-mac-64-nopt-t
http://buildbot.rust-lang.org/builders/auto-mac-64-nopt-t/builds/5319

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#26154 (comment).

[bors]

⌛ Testing commit e87c62f with merge 37cf025...

[bors]

☀️ Test successful - auto-linux-32-nopt-t, auto-linux-32-opt, auto-linux-64-nopt-t, auto-linux-64-opt, auto-linux-64-x-android-t, auto-mac-32-opt, auto-mac-64-nopt-t, auto-mac-64-opt, auto-win-gnu-32-nopt-t, auto-win-gnu-32-opt, auto-win-gnu-64-nopt-t, auto-win-gnu-64-opt